555 HP: GM's New V8 Duramax Is A Beast, But Its Torque Is The Real Story

We now have power ratings for GM's monstrous 8.3-liter turbodiesel Duramax V8 engine, dubbed "The Mongoose." It has 555 horsepower, already beating competing Cummins and Power Stroke engines, but you don't buy a diesel-powered truck for horsepower ratings (although high horsepower is certainly nice), you buy it for torque. As such, the Mongoose is also a Power Stroke killer in that department; GM has announced that it makes 1,230 pound-feet of torque, beating out the high-output version of the 6.7-liter Power Stroke by a scant 30 pound-feet.

All told, that gives the 2027 Silverado HD and GMC Sierra HD trucks a maximum towing capacity of 20,000 pounds if you tow from the hitch, or 38,000 pounds if you opt for a gooseneck configuration. For what it's worth, the new GM trucks actually lose to the Ford Super Duty's maximum 40,000 pounds with a gooseneck, but winning most of the numbers game is still no small feat.

According to GM, torque and diesel trucks are serious business, making up 60% of HD truck sales. However, sharply rising diesel prices during the latter half of 2026 may put a damper on the turbodiesel fun for 2027 model year trucks; but for now, at least, the specs are impressive. 

HD truck buyers who don't want diesel are still invited to the party, too, as the new sixth-generation gas-powered 6.6-liter V8 is standard. It has 412 horsepower and a still substantial 472 pound-feet of torque. Both engines are paired with a 10-speed automatic Allison transmission. 

For the new 2027 model year, the rest of the truck (like its smaller brethren) gets a host of upgrades, like quieter electric power steering and braking, and an updated chassis for better towability and livability. Towing, raw power, and diesel engines get top billing for the newest GM HD trucks, just don't expect them to be cheap to fuel.