Wordless Wednesdays: Rolling Coal In A GMC Sierra HD 0 by Manoli Katakis — Aug 22, 2012 Share This formidable GMC Sierra belongs to Andrew Karker, according to the GMC Facebook page. Congrats to Andrew for an awesome truck! GM Authority is hiring! Submit your application today! — Manoli Katakis Manny is the lead GM Authority writer and provides on-site coverage of GM events as well as road tests of GM's new products.