The Environmental Protection Agency has yet to release its official highway, city and combined fuel economy ratings for the 2020 GMC Sierra 2500HD with the 6.6-liter L5P Duramax diesel V8 engine, but a recent road test conducted by Cars.com may give us a rough idea of what to expect.
The publication put its 2020 Sierra HD test vehicle on a 208.1-mile loop in Michigan, taking the AT4-equipped truck on both city streets and out on the highway. It was a near-perfect day for this test, with the weather perfectly clear and sunny and the ambient air temperature sitting at a crisp 60 degrees. The truck also stayed in two-wheel drive mode for the entire duration of the experiment, speeds were kept to within 5 mph of the posted limit, and acceleration and braking events were carried out in a smooth and consistent manner, Cars.com says.
While the trip computer in the truck showed an average consumption rating of 19.6 mpg, the truck consumed 10.453 gallons of fuel over the 208.1-mile trip, placing its real-world fuel economy at 19.91 mpg. A Duramax-powered 2020 Sierra 2500HD without the AT4 package may be able to achieve even greater fuel economy, as the trim comes with off-road tires that may increase the truck’s rolling resistance as opposed to regular tires. In addition to the off-road tires, the AT4 package also adds underbody skid plates, Rancho off-road shocks, an Eaton locking rear differential and an Off Road setting for the traction control, among other small items.
If you need a refresher, the 6.6-liter L5P Duramax diesel V8 is rated at 445 horsepower and a meaty 910 pound-feet of torque. We imagine the Allison-branded 10-speed automatic, which is the only available transmission on Sierra HD models, massively helps with the truck’s overall fuel economy.
When we tested the 2020 GMC Sierra AT4 2500HD earlier this year, we said we were “pleased by the Duramax engine’s power delivery, smooth and free of unwanted turbo lag.” We also noted that the Allison-branded ten-speed automatic transmission was also a gem as it always seemed to find the proper gear and downshifted smoothly when applying throttle.”
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Source: Cars.com
Comments
Your not going to get a whole lot better than that. I can see 3 mpg maybe. The tires had some play but having a truck that big and high off the ground, aerodynamics are like a brick in the wind. But that’s ok people by these trucks for towing, payload capacity and having a nice rig. I don’t think we will see the days where you could get 25 miles easy from a dually like the other early 2000’s with all the restrictions. Not without getting electrification involved, which could be a interesting.
Well its better than my 2017 L5P.
My 2020 Denali L5P is at 15.5 all around average, but on the road at 65 MPH with no wind was running around 24 to 26.
My 2017 Denali L5P was 12 all around and around 18 on the 65 MPH roads.
I have not driven the 2020 enough yet but where I have driven it the same rout as the 2017 it is better.
So I am again so much happier with this 2020 over the 2017 HD.
Other than the dash center stack look, this 2020 Denali HD is a great, great, awesome truck.
Different axle ratio and transmission in the 2020 are a significant improvement over the 2017. The 18 and 20 in wheels also have slightly larger tire circumference. Our new 2020 with 18’s has suffered from tire uniformity induced rear axle shake, 65-75mph, took some effort at a dealer to road force match new tires to the trucks aluminum wheels, but is acceptable now. Most our previous HD are steel rims and didn’t suffer as much from tire uniformity
Homer i just bought a new 2022 Denali 2500 6.6 duramax the computer says its only getting 13.8 to 15 mpg do you think it will get better only has 450 miles on it
Haven’t tested in90 + high humidity with Windows open no air.And Windows closed and air on. Less fuel economy with out 60 degree cold sir charge.
The EPA NEVER EVER test vehicles rated at 8600 lbs or above GVW…so you will not see any C/K 2500, F250, or Ram 2500 3/4 ton or above pickups with mpg ratings.
You guys really need to do your homework on these topics before posting these articles.
For a truck that weighs over 7,000 lbs and is geared for towing and work, that’s pretty good fuel economy
An exhaust Regen within the measurement period will effect the reported fuel economy. If the truck PUTC tested was new and started with less than 100miles on odo, the truck likely did not experience a Regen cycle in the 208 mile loop. Regardless, the almost 20mpg reported for this configuration, even without a Regen, is excellent.
Tflt (not that they are scientifically correct with their tests) got 20 mpg with a new Silverado 2500. That was before the engine wore in. Probably will get 21-22 mpg once wore in with a normal truck. Still, imagine the off-road range of the at4!
The EPA will not release official mileage numbers. Do to its high GWWR it’s exempt.
Our experience with diesel vehicles is that they typically deliver better mileage with more miles on the engine. Our 2015 V6 turbo diesel Sprinter, tall van (9’3) regular wheelbase achieved a remarkable 25 mpg, over our last 3000 trip into Alberta, Canada. That was achieved with 6 people, foot down, loaded with extra food & fuel, AC & lights always on and with some serious elevation changes.
This truck, I’d expect to improve with time and with better tires. Although, with this much HP and Amazing Torque, it is already amazing.
You lost all credit as a credible source when you said the EPA hasn’t released ratings yet because they won’t ever release ratings for this vehicle.
I have 4 Duramax Trucks. I just bought my 5th which is the 2020. I pulled a piece of equipment to North Carolina and back that weighed 5000lbs. I traveled a total of 825 miles. I burned 5 gallons of def and got 8.4 mpg. The exhaust brake is very weak and the seems to lack power in first and second gear. Not happy at all. Taking the truck to the dealer.
Can I ask what Duramax you have? I have been looking at the 2021 3.0L.
I bought a 2020 3500 dually Duramax .I have put over 12,000 miles on this truck all while towing trailers with combined trailer and load weight of less them 10,000 pounds and I am averaging 6.3 mpg and using 4 gallons of DEF every 1200 miles. I took the truck to 4 different dealers and was told that there was nothing wrong with the truck that 6 mpg is what I should expect while towing. I will be trading off this gutless pig for a Dodge . The Chevy 3500 Duramax is too high geared and is constantly shifting just to maintain the speed limit while towing lite loads.
I had the same problem with a Chevy. The truck was lock in 4 wheel drive. Transfer box only. Does your crash detection come on when u get close to someone in front of u? If not then your truck is in 4 wd. Call I will tell u about it. 7703773848
Would say Johnny is most likely a salesman at a Ram dealership as I have the SRW version of the 2020 and I get over 10 MPG pulling a 14000 lb fifth wheel through some of the steepest grades in the US and 19-21 when not towing.
I just purchased a 2021 AT4 with the 6.6 Duramax. I love the truck and the power but I am getting 12.2 avg mpg. Getting around 15.5 on hwy and 10.5 city. And I do not have a heavy foot. Only 2k miles on truck but if it doesn’t get much better it’s going to get a new home. I know of some big rigs getting 9mpg hauling freight. Very surprised based on the research I did before I purchased.
I had the same issue. I took the truck and found out the transfer case was stuck in 4wd. The front tires were not in 4wd just the transfer case.
Thanks for sharing and letting me know. Amazing that they found that. I asked a local dealer and they told me that couldn’t do anything about the mileage. But I’m going to press the issue this week.
Kind Regards,
JD
I just bought a new 2022 GMC Denali duramax the truck computer says it is only getting 13.8 to 14 mpg it only has 450 miles on it does anyone else have one thats is getting better than i am and what can I do to get more mpg ?
Thank you for replying back bud i have a friend who has the same model and his was only getting 12.5 he got 600 miles on it and his mileage went up on a trip to 19 mpg so maybe mine will do the same
I have some observations I’d like to share, just to add my 2 cents. I love my 2021 GMC 2500HD SLT Crew LP5 Diesel, stock tires, raised camper cap shell, at present 15K miles. Bought to pull my 6500LB 26ft Travel Trailer through the mountains. my 2017 1500 could do it but maxed out and while not over GCVW drive axle always was, also braking challenges on hills. Empty I can get 22 at 70 mph on flat highway, at 65 I can get 24. I average 17-18 on trips with starts and stops, through cities and country. Yes it will depend on terrain, tires, model of truck and overall weight, and air flow around trailers. The AT4, the 3500, and dully will not get as good of fuel mileage as the 2500 SLT. on a 3000 mile round trip from MO to FL with a 3000LB total trailer weight I averaged 13.5 MPG, my 1500 was 9 mpg at best. But it’s not just about weight, but air drag. I do believe once the motor is broken in will do better. I have not hauled my Travel Trailer yet but will be doing this soon, possibly can update this for you folks. I was looking to find out what best RPM speed combinations are, as I have been keeping a diary of sorts, noticed there are groupings of MPH for each MPG and sweet spots for each. Regen will drop mileage too, but that’s just the quirks of owning a diesel. Love the power. As far as the exhaust brake, I found it to be quite effective. Granted only 3000 lbs but it will stop you the more you apply the brakes, and yes uses transmission downshifts. Truck does the thinking for you. Manual tells you how to make it work best. For max results, Tow Haul Mode, and in Cruise. We have a curvy road with steep truck down grades going one direction near my house, goes 7-8 miles. With exhaust brake on, I would use the cruise switch on the steering wheel to toggle between 45 and 25 mph based on curves and truck grades. I never touched the brake pedal the entire road till I got to the stop sign at the bottom. WOW, was I impressed. No trailer but does work. I tried it on my return trip from FL and it worked even better with tow haul mode in even though I had trailer weight this time. Hope this gives some encouragement to those of you currently disappointed with your truck. I really like mine. Can’t wait to take it up and down the Eisenhower in CO. I plan on setting the cruise and never touching the brakes.