New GM Duramax 8.3L Diesel V8 Delivers 555 HP for 2027 HD Trucks

• GM’s new available Duramax 8.3L Turbo-Diesel V8 produces 555 horsepower and 1,230 lb-ft of torque, numbers that beat every diesel engine Ford and Ram currently sell in a heavy-duty pickup.
• The 2027 Chevrolet Silverado HD and GMC Sierra HD also switch to electric power steering and a new brake-boost system, changes GM says sharpen low-speed control and cut noise.
• The updated trucks reach U.S. dealers late this year, though GM has not released pricing yet.

The New Diesel Beats Ford and Ram on Paper

General Motors has never built its own heavy-duty diesel engine from scratch. Every Duramax that has gone into a Silverado HD or Sierra HD traces back to a joint venture with Isuzu. That changes for the 2027 model year. GM designed, developed and builds the new 8.3L Turbo-Diesel V8 in-house, and the company says the work shows in the numbers: 555 horsepower and 1,230 lb-ft of torque, the highest figures of any diesel pickup engine on sale.

Those numbers matter beyond bragging rights. A properly equipped Silverado HD or Sierra HD with the new engine can tow up to 20,000 pounds on a conventional hitch and up to 38,000 pounds on a gooseneck, GM says. Buyers who haul horse trailers, RVs or heavy equipment for a living get the biggest benefit. Those tow ratings mean fewer trips and more margin when a load runs heavier than planned.

How It Stacks Up Against Ford and Ram

The heavy-duty truck fight has come down to a horsepower and torque arms race, and GM just took the lead on both counts. Ford’s High-Output 6.7L Power Stroke, the strongest diesel in the Super Duty lineup, makes 500 horsepower and 1,200 lb-ft of torque. Ram’s High-Output 6.7L Cummins tops out at 430 horsepower and 1,075 lb-ft, though it still claims a maximum tow rating of 36,610 pounds. GM’s 38,000-pound gooseneck figure edges past that too.

Numbers on a spec sheet only tell part of the story. Ford and Ram both have years of real-world durability data behind their high-output diesels, and GM’s engine has not towed a single trailer in a customer’s driveway yet. Fleet buyers and tow-heavy shoppers will want to watch early reliability reports before they read too much into the launch figures. Still, more than 60% of heavy-duty buyers already choose a diesel engine over gas, GM says, and the company already holds the largest share of that group. A genuine horsepower lead gives GM a reason to keep those buyers instead of losing them to a Super Duty or Ram 3500 showroom.

GM is not walking away from gas buyers either. The 6.6L gas V8 offered alongside the diesel now makes 412 horsepower and 472 lb-ft of torque, which GM calls the strongest standard torque figure among 2027 heavy-duty gas engines. For buyers who tow occasionally rather than daily, that engine costs less to buy and to maintain than the diesel, even with the power deficit.

Steering and Braking Get an Overhaul Too

The engine gets the headline, but two other changes affect daily driving more directly. GM replaced the hydraulic power steering pump with a rack-and-pinion electric power steering system, a first for a heavy-duty pickup in this segment. GM says the new setup produces roughly 30% more steering power than the outgoing hydraulic gear, which should translate into easier low-speed maneuvering around a job site or a crowded parking lot when a heavy plow or service body sits on the front axle. The electric system also drops the pump, hoses and fluid that hydraulic steering needs, which GM says cuts noise and long-term maintenance.

Braking gets an equally direct upgrade. A new electronic brake-boost system pairs with larger brakes and four-piston front calipers, a combination GM says delivers steadier, more consistent stopping when a trailer adds thousands of pounds behind the truck. GM also expanded its drive-mode software, adding a Terrain Mode with one-pedal off-road control that the company says has never appeared on a GM heavy-duty truck before, along with revised Tow/Haul and Off-Road calibrations.

“For 2027, we took GM’s proven HD validation playbook and turned up the capability, integrating new powertrain, braking, steering and chassis technologies for serious customers who push their trucks hard every day,” said Mark Dickens, Executive Chief Engineer for GM Full Size Trucks and SUVs. “HD customers don’t hold back, and neither did we.”

Pricing and When You Can Buy One

GM has not released pricing for the updated Silverado HD or Sierra HD, and the company says MSRP and further product details will arrive in a future announcement. For context, the current Silverado 2500HD starts at $48,195, and adding the outgoing Duramax diesel adds another $9,990 on top of that. A new in-house diesel with a horsepower advantage over Ford and Ram gives GM little reason to price the 2027 trucks any lower.

Both trucks arrive at U.S. dealers starting late 2026. Shoppers cross-shopping a heavy-duty diesel this year face a real choice: buy a proven Ford or Ram with an established repair network and known reliability record, or wait for GM’s new engine and steering hardware to reach dealers and hope the on-paper advantage holds up once real trucks start racking up miles.