In addition to a class-action lawsuit surrounding General Motors’ eight-speed automatic transmission, GM faces a pending class-action lawsuit over what owners have deemed the “Chevy shake.” However, GM lawyers have begun their arguments in court to move to dismiss the pending litigation.
Carcomplaints.com detailed GM’s response to the lawsuit and said it’s a “classic example of overreach.” In the lawsuit, the plaintiff alleges his 2015 Chevrolet Silverado experiences vibrations and shaking within a year of owning it. Specifically, the shake becomes violent between 75-80 mph. The plaintiff took his Silverado to a Firestone to have the tires, rotors, brakes replaced, a realignment, and the wheels re-rounded. The shaking persisted and the plaintiff returned to the store months later.
Eventually, he made an appointment with a dealership, which told him the shaking was due to the brake rotors, even though they’d been replaced. The dealer also said the vibrations “were within normal limits.”
GM poked at the arguments made and said the plaintiff didn’t seek out answers or possible repairs until 19 months after the Silverado allegedly began to shake. Although the repair supposedly didn’t fix the problem, GM noted the plaintiff waited three and a half months before trying to remedy the issue again.
“Throughout the entire 27-month period between the time in which Plaintiff claims he first experienced the shaking to the time when Plaintiff first sought repair at an authorized GM repair facility, Plaintiff does not claim that he was unable (or unwilling) to drive his vehicle,” GM lawyers argued.
Further, GM lawyers said the plaintiff is unable to make arguments that every other Silverado, Sierra, Tahoe, Suburban, and Yukon also house the defects. GM pointed to other cases where lawsuits were tossed out as plaintiffs made assumptions about vehicles he or she never owned. Finally, GM noted there is no breach of warranty because the plaintiff does not have evidence that “the Silverado was not fit for its intended purpose of providing transportation.”
GM also dismissed the notion it knew about the “defect” ahead of time and evidenced the 109 complaints filed surrounding the “Chevy shake.” Only 24 were made before the plaintiff’s problems and just seven of them refer to the Silverado specifically.
The pending lawsuit alleges the aluminum driveshafts are the source of the issue in the vehicles and cause the shaking. Only a custom-made steel driveshaft fixes the problem, per the documents. The plaintiff and the class-action lawsuit argue for reimbursement for out-of-pocket repairs.
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Source: Carcomplaints.com
Comments
GM doesn’t deny the truck shakes as alleged between 75-80 which is legal speed in several states. GM seems to be saying just drive slower. Do Ford trucks have this problem?
Yes. My 2016 F-150 did and they couldn’t get itbto go aeay. They told mebit was within their spec so they wouldn’t do any more for me. The Super Duty’s have had vibration problems for a looooong time.
It can’t be a common occurrence because the three 15 Silverados that my family owns don’t get the shakes until about 110 MPH. And that’s not a problem because my 13 Malibu doesn’t even accelerate past 90 MPH, despite only being at 3500RPM at 90 in 6th.
I have a 2018 Colorado that vibrates at different speeds. The dealer replaced the torque converter stating GM has had problems with this vibration in Canyons and Colorados in Florida and Texas. Something about the oil inside the converters. After replacement the problem was solved for about four months. It has started again and I have to make an appointment with the dealer to address the same problem a second time.
The issue with your truck is actually the transmission fluid that they’re using. It was discovered that that new fluid caused quite a few issues in a lot of vehicles GM was just the first to start using it. I believe they’ve either released an updated fluid or other people have gone back to an older version of ATF had no problem
This is your issue. The new fluid will fix the shudder for good. The previous fluid (fluid available up until a few months ago) had an issue with moisture absorption that would cause the torque converter clutch to shudder.
https://gm-techlink.com/?p=11127
J have a 2019 Colorado and had the fluid changed to the Mobil 1 fluid they stated would fix he problem. and guess what, the shake returned 11,000 miles later, now they are saying it’s the converter….I have my doubts. i filed a complaint with the NHASB, but found out i was the 56 person to file. i was told they need 700 or more complaints that could cause harm to people before they can offer a recall on the vehicle…. I don’t know if this is true.
I have a 2018 Colorado also with the shakes/shudders and it’s off and on at pretty much any speed and it’s getting worse…the vehicle only has about 8700 miles on it. Going to make an appointment with the dealer next week and see what happens.
My 2014 Silverado had that same problem. One of the many reasons I got rid of it
Had my 15 Sierra well over these speeds many times and have zero vibrations. I don’t know how these people with issues drive their truck, but I’m not particularly easy on it. My dad has a 15 Silverado with the V6 and has no issues either. Sometimes I think people just want to complain about something. Which for the prices of these beasts you’d expect no problems, but still.
I had a 2015 Silverado with the exact same issue. Dealers told me I would have to pay for a road force balance. I called corporate too. They all denied that issue exists. Now I see this article!
I had 2014 Silverado Double Cab LT with the same issue and that is why I traded it. It got so bad it sounded as if the back window was down and one of the tires was seriously out of round
I have a 2012 Chevy avalanche and my vehicle is shaking as well during acceleration and I’ve replaced upper and lower control arms engine mounts etc. still shakes. Sadly same thing happen with my moms 2002 Chevy avalanche. I’m just gonna sale it to car max this is ridiculous.
My father had the same problem and took his truck to the dealership no less than 6 times. He asked for paperwork detailing what had been done to alleviate the problem and was told that they could not provide it because it had to be mailed to him. He never received any documents in the mail. The last time he took it to the dealership he was shown a document that now stated that the shake was normal according to manufacturer specifications and he was promptly ushered out the door with no remedy. This took place over the space of a year. The truck was approximately 1.25 years old at this point. My father gave up and traded the truck on a new vehicle.
My father had originally purchased this vehicle for towing a camper that would be going on a trip from West Virginia to Alaska. He put off going on that trip for a year due to the problematic shake. He is currently on this trip with a new truck.
The dealership was right: Chevy determined that the shaking was “normal” for these trucks (not Ford or Ram) and therefore just live with it and drive slowly. The GM 8 speed trans has similar “normal” issues that cannot be fixed and GM is just phasing it out now.
I don’t know where you got the idea that Ford and Ram don’t have “normal” or “acceptable” levels of vibration. All manufacturers do. Ford told me the vibration in my 2016 F-150 after trying all the cheap fixes they could. My truck still had a shake on the highway and Ford told me it was within spec. A basic Google search shows that every manufacturer has complaints for vibrations. Most manufacturers just never get publicity like GM did on the issue.
https://www.lemonlaw.com/wordpress/ford-f-150-vibration-continues-leave-drivers-shaken/
God I’m so tired of these I knew a guy with an issue stories.
@ArcticDog – Troll much???????
I’m not sure of what you would accept as proof. Do I need to provide photos, vin, and video? I posted only because the story struck a chord with me. I have been with my father when the shake was happening so this is from first hand experience of the problem.
Sounds like you neither know what a troll is or what first-hand experience is. First-hand experience would be me owning a 2018 Silverado and stating that I’ve not had any issues like that.
I’ve read other people do. But I see far more “I know a guy that had this issue this issue this issue.” It causes a relatively small problem to get blown completely out of proportion. Welcome to the internet.
The plaintiff has no idea what’s causing his issue, he just paid Firestone to throw money at it when they clearly didn’t know what was going on. now he read something on the Internet where someone needed a new driveshaft and he thinks that’s his fix too but he has no freaking clue.
I hear some of these trucks have issues. My 2018 is very smooth, but just because mine is smooth I won’t say all of them are just like he shouldn’t say that all of them have an issue.
My 2017 Silverado shakes between 70 and 75 mph. If I inflate tires two psi above recommended it reduces the shake but does not eliminate it.
If I put 4 midgets under my tonneau cover and have them roll back and forth while I’m driving down the highway it makes the truck seem like one leaf spring is longer than the other, but if I put alligators in the bed instead of midgets it makes it seems like one leaf spring is shorter than the other. The only thing that fixes it, I read in my favorite nsfw Chevrolet forum, is to put seafoam in the ashtray while flooring it and holding the lighter plug in.
Funny, but not a comment from the original Homer on GMA
My 2018 Colorado shakes at any speed if you have to slow down and then get back on the gas. Dealership says that it is “within normal range”. This is the first vehicle I have ever owned that had an allowable range for a vibration. New trucks shouldn’t have those! Also had to have the carrier bearings replaced at 14000 miles. Thinking maybe a Tacoma soon. Colorados are junk!
Ditto. 2014 Silverado
Every manufacturer has a spec for acceptable vibration. My 2016 F-150 had a vibration that thevdealer and Ford engineers couldn’t fix with wheel replacements, tires, a dozen attempts at road force balancing, new driveshaft, etc. They gave up eventually and said it was within spec and sent me on my way. The 09-14 F-150’s had vibration problems in some configurations as well.
Carrier bearing at that age says there is a problem with driveshaft. Think about how it works.
I have a 2014 Silverado and it shifts and clunks like crap. I love my truck but I really wish GM would put more care into the transmission and drive line to give a smoother, less clunky acceleration and deceleration. Or PLEASE make more manuals so they are easier to get.
Glad you mentioned this i have had 14 with same clunky shifting traded in to a 16 and same thing they never start that way dont really notice until after 40k had a tranny flush and new fluid no difference..did you try anything else to help?…..kills me that my 06 with 179k is so smooth
The harder it shifts, the longer your tranny will last. Uncomfortable truth.
I have a ’15 Silverado crew cab 5.3 and have no vibrations at all. For the longest I’ve heard of vibration issues but never experienced it.
It’s because of the roads. People don’t get certain roads are supposed to grip tires and cause it no matter what truck. Same people just want cheap trucks and thats why they flock to cheap rams.
Had a shake at 75mph in my 17 2500hd gasser. Tires needed balanced and problem solved. Great truck since and that was 20k miles ago.
I owned a 2014 Sierra that vibrated excessively at 72 to 78 mph. Yhe dealer says they could not replicate the problem so basically FU. The resolution was to trade lt for a 2019 Ram 1500 and voila – same roads same speed and smooth as silk! Loving my Ram for many more reasons. More truck better truck less money.
My 2014 shook at 70 miles an hour. I traded it in on a Ram 2500 and couldn’t be happier. I got 28,000 miles on my Ram and not one single problem.
You clearly aren’t a truck guy if you think a Ram is a big improvement quality wise. FCA produces the lowest quality vehicles out there.
Uh, the recent Dodge Rams were named “Truck of the Year” by Car and Driver if I recall two years in a row! They have power, a smooth ride, and the interiors are better than Ford or Chevy! Yeah, they’ve improved a lot in recent years! Their weak point is fuel mileage avg but is still a big truck seller, only slightly behind the Ford 150, which has been declining in quality in recent years.. Check Edmunds or other vehicle sites.. and yeah, no “shake” problem like Chevy or Ford trucks!
I just traded in my 2016 silverado 1500 because of this. Spent 3500 in repairs cause it had been lifted by the dealership which voided my factory warranty. The extended warranty wouldnt cover it because it was still within the factory warranty mileage so I got stuck with the bill. Then after that bill I had to get new tires and rims because it was still doing it. After a couplt of months on the new tires it came back setting off all the sensors on the block. Dealership wanted to change out all the same parts again said no.
My daughters 15 z71 shook from day one they replaced ring gear and pinion tires brakes shocks drive line and never fixed it
We’ve had three Silverados. An 01, 09, and now a 2018. This truck has horrible clunking, shudder, and vibration. The 01 and 09 were great trucks, not this one! Dealer says it’s caused by too much road force. Since I can’t find less forceful roads it can’t be repaired. Can’t wait for the day someone totals the truck or the extended warranty runs out so I can say goodbye to Chevrolet! Not sure which manufacturer we’ll pick next time but I’m POSITIVE which manufacturer we wont! Chevrolet should have employees that do nothing but read forums like this and perhaps they’d get the picture!
So uhm why do people keep buying these trucks? They’re obviously junk. Buy a Toyota. They seem to be the only manufacturer who can build anything that works properly as an automobile or truck these days.
Buy a Toyota. GM should have gone out of business years ago. From the Northstar head gasket debacle to the dexcool nightmare. Not to even mention the body rot issues. Stop buying this junk. This is not the Chevy of the 1970s
Had a 2015 Sierra that would shake at 60+ MPH, it was the Goodyear tires that came with the 20″ Texas Edition rims. Those tires were junk and the dealership knew it, one guy had to have 4 different sets replaced because they were all out of round. I had several replaced but when one was replaced another would need replacing. The dealership would not put a different tire on there for warranty reasons.
I have owned 14 new Silverado 1500’s in the last 5 years and have not had a issue with one of them ! I had one that had a vibration but it was because of a wheel weight coming loose .. went to the dealership and 15 min later it was fixed
I have a 2017 GMC Denali 3500 HD dually w 148,000 miles and smooth as silk – never a shake. I know a number of folks w ’15 half tons who’ve had no issue with close to 100k miles.
My 2015 shook horribly at highway speeds when I bought it, tried having the wheels balanced several times and had my driveshaft checked and nothing fixed it. Ended up replacing the OEM Goodyear Wranglers for Firestone Destination LE2 and the shake is gone.
I have a 2017 Silverado that bucks and jumps at 50 to 70 mph because of the drive by wire throttle. Put plywood between the plastic mount for the throttle and the firewall which helped some. Power steering quit when I hit a small bump in a parking lot. The dealer took days to fix that. Wish I had my old truck back. Would not take this junk off road or mountain drive for any amount of money. Chevrolet could care less about the problems. Cannot trust it to get me there and back.
GM simply doesn’t care about your problems with THEIR vehicle once it leaves the lot. Not a Silverado owner, but the Colorado zr2. Was my dream truck that turned into the worst ownership nightmare I have experienced, and I have had quite a few different vehicles in my time. If it’s not the horrendous constant rear end clunking and squeeking, it’s the catalytic converter going out, or rattles in the motor, or transmission SLAMMING into and out of gear, or more recently, the inability to remove your key from the ignition, etc etc etc… I am so over this. It’s been in for repairs so many times I have lost count, and the best part is it is usually worse in some way once I finally get it back and GM corporate as well as dealership just tell me it’s a normal Chevy thing. None of my 200000+ mile Tacoma’s ever sounded this beat up and I have less than 30k on this POS. Don’t waste your money and mental health, buy a Toyota. Or anything else for that matter…
I have a ’12 Silverado 2500HD in addison to my ’17 Denali dually – both Duramax/Allison. The only prob I’ve ever had in nearly 150k on the Denali is an aluminum trans line that rubbed through on a steel bumper support at 50k fixed by the dealer. The Silverado has had issues related to engine mods – not factory issues. Also own a 2004 half ton 5.3 that pulled a 9k fifth wheel like a champ. Also know dozens of RV transporters w literally hundreds of thousands of miles on HD GMs with no issues. Seems like a number of folks commenting here should be able to lemon law their vehicles if they are truly having these serious issues.
For the love of God don’t run them in 4WD on dry pavement. Most of the folks who have complained to me personally don’t know the difference between AWD and 4WD. I have a 2018 Sierra HD and 2018 Yukon XL both Denalis with no problems.
Currently have a 18 Silverado Regular. Had to call GM to force dealership to look at the Chevy Shack issue. The dealership technician acknowledges the “Chevy Shack” issue. That it is the chassis from 14-18 model years and the problem is most notable on the short cab (regular). Already replace two tires and rotated. Less noticeable. But still there. However the 19 Silverado Dble Cab “loaner” drives awesome.
2016 GMC Denali
Vibrates like crazy and does it regularly and consistently. Rotate and balanced tires, brakes and rotors are fine.
Beautiful truck, drives like crap.
I bet GM’s lawyers don’t drive GM trucks!
2018 Silverado LT Z71 Crew 4x 4 Truck with 11k miles is currently at dealer for 8 days. They tried to say it was within spec and I refused to accept that and filed a claim with Chevy that night. Today 8/6/2019 the dealer called said the tires were forced balance and the tech agreed that the vibration was their and they were going to start replacing tires. Still no call from a Chevy rep from filing the claim. The dealer said they would force balance the tires and use pico scopes when I dropped it off on 7/29/19 but never did any of that until I filed the claim on 8/5/19 after they called and claimed the truck was in spec and I refused. It seems to be they are now only looking at it since I filed a claim with Chevy or they could be stalling.
The pain is real. Two trips to dealer they tell me they can’t find nothing. This trip they take me on a test drive and tell me how terrible it is and not to drive it at high speed. They took it and checked tires at 28,000 miles and won’t release truck because of safety reasons. Now they say I have to buy tires before they release it. Thanks chevy wish I could post picks.
I have a 2012 GMC Sierra and was having the same issue about a year. Changed the tires no help. Changed the rims no help. Checked the drive shaft balance no help. So i took it into Christian Brothers Garage and guess what they found the problem. In my case there was one side of the motor mount on left side broken. They change the left motor mount and to my surprise my GMC now runs smooth at all hwy speeds. Before the motor mount change my truck would shake a lot at around 60 to 70 mph. Hope this might help someone else to check theirs.
I just made an emergency purchase of a 2017 Chevy Colorado tonight. Our older Suburban was on its last legs and wasn’t worth the $8000 to replace the beat up old engine. As such I had no time to research and was unaware of this ongoing issue with several 2016 and new models. I went with the Colorado as I used to drive one for work and of all the small trucks I’ve had it was the hardiest with the exception of my 1995 Toyota Tacoma. The truck test drove completely fine. I noticed the shudder for the first time as I was accelerating up a hill approaching the freeway. The truck has less than 11,000 miles on it. I immediately pulled over and called the dealer. They will be checking into it on Monday and I will try to remember to update with progress on correcting the issue. I am hoping that GM decides to stand by their customers and fix the issue correctly.
I have a new silverodo 2019 new body style, I’m getting a low speed vibration slowing down starts at 40 mph if you hold speed at 4o mph it will vibrate also. I Orignally would say a back rotor. Dealer says it’s there but acceptable. Any body else notice that. I drove a 2020 does it also has same issue. They both have eight transmission
Yes, my 2019 silverad cree cab z71 has some Kind Small vibrations at 40 miles per hour. My brother has same exact truck and same exact vibration.
I’ve liked Chevys all my life, after buying my 2016 High Country Silverado and having the Chevy shakes, I no longer am a fan of Chevy trucks.
I’m switching to Toyota trucks. Goodbye GM!
2017 chevy silverado shakes like crazy at 65mph cant use cup holders too much noise.
2014 Silverado shakes at highway speeds. I either have to speed or piss people off cause I can’t drive 60-65 like everyone else. 55 and under or 70+ are my options. Dealer back in 2014 basically told me it was normal and there was nothing to be done about it. I had buyers remorse for a long time, especially since this was my first brand new vehicle purchase and I could read of the issue happening to others and GM seemed to care less. I have always had used vehicles. I could have chose any truck and I chose GM. Still feel so burned I made this purchase. Been 6 years of this shaking crap. Worrying about coked up valves as my mileage slowly drops over time and AFM valve failures, shoddy feeling transmission, OMG the transmission feel is horrible. Learn my driving style, yeah right it still hasn’t learned after 6 years. I could go on about other issues common with these trucks. I often wonder if I should have went with the 2014 F150 with the 5.0 I test drove. I had an older F150 with the 5.0 and the E4OD and it was a gem. Almost 200k and it never had a major issue other than rust here in NY.
My 2019 Chevrolet Colorado rolled backwards over my entire body. I was on the passenger side vacuuming my truck and I pulled my keys out of my ignition and the truck began rolling backwards, knocking me to the ground. I suffered a broken tailbone, pubic bone and hip was all fractured. I had a puncture lung with a blood clot in my lung. These vehicles are not safe! I’m terrified each time I get in my truck. I purchased this vehicle March 2020, and I took it back to the dealer the 1st week, due to the shaking and transmission problems. I still have transmission and shaking issues. I’ve been back to the dealer 3 times. I’m seeking an attorney to help assist me with my case.
2015 chevy silverado high country shakes between 70mph and 80mph. I have truck two different chevy dealers, Firestone, change tires and rims. Vibration still there
I had a bunch of Chevys so I got a new one and it was junk and the paint peeled off. Since it was worthless from almost the day I die drove it off the lot brand new and it also had the excessive vibration even though I tried taking very good care of it. They blamed the paint peeling off on me… can you believe it. I’m so glad I gave that truck away and everything’s better now.
Bought a used ’15 Silverado 6.2L with 8-speed tranny (73K miles). Reviews I’d read said nothing about this shake. At first, I thought it was the T/A tires or stiffer ride than my ’03 Tahoe (Lord do I miss that vehicle now!). Shake occurs around 1.5K RPM at light throttle, just as described here and other forums. Will chase the “driveshaft” possibility with my old mechanic. Can’t believe the number of posts related to this issue.
Update: Turns out my “shake” was fixed by draining / re-filling tranny with new fluid. GM Service Bulletin 16-NA-175, Feb/2019. Problem was resolved with this repair action.
I had to flush the torque converter and it stopped for a while. About 5k miles later the shake returned. They had to replace the torque converter and that stopped the shake. Turns out the transmission fluid was turning to a sludge and was settling in the torque converter.
becareful, that may solve the issue temporally. We were told my truck was flushed at 19,000 by the dealership (before I purchased it), I’m now at 68,000 miles and its shaking again. No I’m being told I need new transmission
I have a 2019 Yukon XL it shakes on 30-40 mph when I let it roll without pressing the accelerator
Once I touch the accelerator it doesn’t shake much
As well when driving on hwy speeds above 70MPH the car will vibrate
I have done wheel alignment and tire balancing and still experience the issue
Dealer test drove and says they don’t see anything wrong
How do I go about this?
It’s just 12 months old with 14k mi
I need to get rid of this shaking it’s just annoying and makes me sick
2019 Yukon shaking after tire balance and after wheel alignment
I own a 2015 GMC SILVERADO IVE DROVE 7 MONTHS EXPERIENCE THE SAME IDENTICAL PROBLEMS STARTED VIBRATION AT 35 TO 60 NOW ITS EVALUATED WAY WORSER TO MY CONSOLE SEEMS AS ITS COMING LOOSE I JUST PUT BACK IN SHOP YESTERDAY DONT MAKE SENSE!!! IM REALLY FUSTRATED WITH THIS
I just bought a 2018 Silverado and the shake is horrible! I can’t believe that you pay all this money for a truck and it has a problem like this!
For those who are having the shake problem , you will find that your truck may have locking lug nuts !
If you remove them and weigh them , you will find they weigh more than others . your truck will always show signs of imbalance because these locking lug nuts put your truck out of balance by 18 grams !
We are having this issue now. Took in my 2018 Chevy Silverado for a recall on brakes back in April. We advised the service tech that the truck shake while driving, he told us it was the rotors and they needed to be replaced. We did not have money to do that so we held off, because of course it was not covered under warranty. Couple of months later, we were able to take it to a local mechanic to have the rotors replaced, who then told us, the rotors were fine and it was actually our transmission. He updated us on this “chevy shake”. We are now fighting with Freedom Chevrolet in Texas because now we need a new transmission but are now out of warranty. My truck is at 68,000 miles… had the service technician caught this issue back in April, we would still be in warranty… a big scam… 3 year old truck, 68,000 miles on it and we are being hit with needing new transmission that GM new was bad..
This is unbelievable! I had a 2017 Chevy Colorado that did the same thing. I took it into the dealer over and over without any solution. I finally traded it in because I was afraid it was going to break down and I’d be left with nothing.
Have them change the fluid and torque converter. That solved my shake.
Chevy Shake FIXED!!!!!
Went thru this on my ~15 Denali 6.2l, stock height. Get up to ~80MPH and let the shaking begin. Mine feels like coming from the back end. My shake will get better and worse while driving, shake a little, then all of a sudden shake real good. Applying brakes while this shaking occurs makes things jump around a bit, unsafe.
I replaced the Mag ride shocks about 2.5 years ago with KYB.
Many times I rebalanced wheels, rotated wheels, road force balanced all and nothing helped. Tried the tire air pressure trick and no real luck. Read thru many threads talking tranni, axles, rotors, torque converter with most not having much luck after these expensive repairs. Tried the increase speed, shift manually into lower gear at speed, no change.
So I figured I was not going down that path already tried, time to look else where.
Noticed exhaust pretty shaky and wondered if this darn thing was shaking while driving causing the issue. replaced factory exhaust hangers with poly ones, no change 🙁 but exhaust not moving around.
FIXED mine finally!!!!
After replacing exhaust hangers and returning from a test drive I stood on one rear corner of the bumper and pushed the truck up and down pretty lightly but enough to get some compression on the shock. Notice some slight “sloppy/loose” reaction from the shocks from a side to side perspective. The truck swayed back and forth pretty easy. I was expecting a little firmer stance. A normal good push on the bumper and you would be convinced shocks are good.
So I purchased new rear shocks since on the cheaper end and easy to do side. New shocks on 2 weeks ago, road test, Rear is all good for 2 weeks now, still no shake. I now feel the front doing some thing but not as obvious as back probably do to weight. Front struts replaced this weekend, Drives like a new truck.
There must be a design issue with the shocks at ride height and how quick/slow they respond to small variations. Seems like when getting to a certain speed, 80, the ever so slight “looseness” is causing a harmonic with the tire and the shock that amplifies the effect. I suspect the shock is going up and down pretty quick causing this vibration. Mine would shake on brand new velvet smooth pavement. This also helps explain changing air pressure and or adding weight to the back seemed to help the problem but not solve.
Good Luck!!