It’s the HD Trucks’ Turn
The 2027 Silverado HD and Sierra HD might not be getting a design makeover like their light-duty cousins, but what’s happening under the skin is just as significant. GM has just announced a seriously overhauled heavy-duty lineup, with fresh powertrains, sharper steering and brakes, and tech that promises to make towing and hauling feel less like a chore and more like a flex.
The spotlight is on 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. Alongside it is an upgraded 6.6-liter gasoline V8 that gets a noticeable output bump without changing its role as the lineup’s standard gas engine.
GMC
A Serious Mechanical Refresh
Instead of a complete visual overhaul, the Silverado HD and Sierra HD receive updates focused on capability. GM says the new heavy-duty trucks were engineered as a complete system, with the powertrain, chassis, steering, brakes, and drive modes all working together for towing, hauling, and off-road driving.
The refreshed lineup also introduces a segment-first rack-and-pinion electric power steering system and an electronic brake-boost setup for heavy-duty pickups. The new steering replaces the previous hydraulic-assisted system and is designed to deliver more precise steering feel, reduced kickback, and quieter operation whether the truck is on the highway or 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 allows one-pedal off-road driving on steep trails.
Chevrolet
Meet GM’s All-New Duramax 8.3-liter Turbo-Diesel V8
The biggest story is the arrival of the Duramax 8.3-liter turbo-diesel V8 called the Mongoose. This replaces the long-serving 6.6-liter Duramax as GM’s flagship diesel for heavy-duty pickups and becomes the company’s first all-new heavy-duty diesel architecture created entirely in-house. The engine was built specifically for pickup truck applications instead of adapting an existing commercial diesel design.
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 for the heavy-duty pickup segment.
The engine features a compacted graphite iron cylinder block, a 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 those upgrades help improve durability while maintaining consistent performance during long towing sessions and steep climbs.
The Duramax is paired exclusively with the Allison 10-speed automatic transmission, along with upgraded exhaust braking and a redesigned aftertreatment system. GM says the combination is intended to improve launch performance with heavy trailers, downhill control, and long-distance towing confidence.
Properly equipped Silverado HD and Sierra HD models can tow up to 38,000 pounds with a gooseneck trailer, while conventional towing reaches 20,000 pounds on select configurations.
GMC
The Gas V8 Gets Stronger Too
Not every heavy-duty truck buyer wants diesel power, so GM also updated its standard gasoline engine. The familiar 6.6-liter V8 now delivers 412 horsepower and 472 lb-ft of torque, giving it what GM says is the highest standard torque rating among 2027 heavy-duty gas engines. Engineers also revised the intake manifold, lubrication system, engine-mounted oil cooler, emissions hardware, and added 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 transmission with revised shift logic to keep the engine in its optimal power band when towing or climbing grades.
GM says the updated Silverado HD and Sierra HD will begin arriving at US dealerships in late 2026, with pricing and additional product details to be announced closer to launch. The heavy-duty updates follow the rollout of the redesigned light-duty Silverado and Sierra, giving both truck families a fresh round of powertrain improvements heading into the 2027 model year.
Chevrolet
