The 2027 Silverado HD and Sierra HD are getting a major mechanical overhaul rather than a full design makeover, with General Motors introducing new powertrains, sharper steering and braking systems, and updated technology focused on towing, hauling and off-road capability.
The biggest change is an all-new Duramax 8.3-liter turbo-diesel V8, GM’s first clean-sheet heavy-duty diesel engine designed, developed and manufactured entirely in-house. The trucks also receive an upgraded 6.6-liter gasoline V8 with increased output while retaining its position as the standard gas engine.
2027 Silverado HD and Sierra HD Get New Hardware
GM says the refreshed heavy-duty trucks were engineered as a complete system, with the powertrain, chassis, steering, brakes and drive modes designed to work together for towing, hauling and off-road driving.
The lineup introduces a segment-first rack-and-pinion electric power steering system and an electronic brake-boost setup for heavy-duty pickups. The new steering system replaces the previous hydraulic-assisted setup and is designed to provide more precise steering feel, reduced kickback and quieter operation on the highway or while pulling a trailer.
GM has also expanded its drive-mode strategy. Tow/Haul and Off-Road modes have been recalibrated, while ZR2 and AT4X models gain a new Terrain Mode that enables one-pedal off-road driving on steep trails.
New Duramax 8.3-Liter Turbo-Diesel V8
The centerpiece of the 2027 heavy-duty lineup is GM’s new Duramax 8.3-liter turbo-diesel V8, known as the Mongoose. It replaces the long-serving 6.6-liter Duramax as GM’s flagship heavy-duty pickup diesel and becomes the company’s first all-new heavy-duty diesel architecture created entirely in-house.
Unlike an existing commercial diesel adapted for pickup use, the engine was developed specifically for pickup truck applications. It produces 555 horsepower and 1,230 lb-ft of torque, giving Chevrolet and GMC what GM claims are best-in-class diesel horsepower and torque figures in the heavy-duty pickup segment.
The engine uses a compacted graphite iron cylinder block, forged crankshaft, forged connecting rods, steel pistons, a high-efficiency variable-geometry turbocharger and a dual-stage air-to-water charge cooling system.
GM says these upgrades are designed to improve durability while maintaining consistent performance during long towing sessions and steep climbs.
The new Duramax comes exclusively with the Allison 10-speed automatic transmission, along with upgraded exhaust braking and a redesigned aftertreatment system. According to GM, the combination is intended to improve launch performance with heavy trailers, downhill control and confidence during long-distance towing.
2027 Silverado HD and Sierra HD Towing Capacity
Properly equipped Silverado HD and Sierra HD models can tow up to 38,000 pounds with a gooseneck trailer. Conventional towing reaches 20,000 pounds on select configurations.
Upgraded 6.6-Liter Gasoline V8
GM is also giving its standard gasoline engine a significant update for buyers who do not want diesel power. The familiar 6.6-liter V8 now produces 412 horsepower and 472 lb-ft of torque.
GM says the updated engine has the highest standard torque rating among 2027 heavy-duty gas engines. Engineers also revised the intake manifold, lubrication system, engine-mounted oil cooler and emissions hardware, while adding a digital oil-level display to improve low-end pulling power and durability.
Like the new diesel, the upgraded gas V8 is paired with the Allison 10-speed automatic transmission. Revised shift logic is designed to keep the engine in its optimal power band when towing or climbing grades.
2027 Silverado HD and Sierra HD Launch Timing
GM says the updated Silverado HD and Sierra HD will begin arriving at U.S. dealerships in late 2026. Pricing and additional product details will be announced closer to launch.
The heavy-duty updates follow the rollout of the redesigned light-duty Silverado and Sierra, bringing a new round of powertrain and capability improvements to both truck families for the 2027 model year.
