General Motors just reset the heavy-duty diesel race. The 2027 Chevrolet Silverado HD and GMC Sierra HD will offer an all-new 8.3-liter Duramax turbo-diesel V8—internally nicknamed Mongoose—with 555 horsepower and 1,230 lb-ft of torque. That is the largest displacement, highest horsepower, and highest torque diesel in a current Big Three heavy-duty pickup.
The same model year also brings next-generation light-duty Silverado 1500 and Sierra 1500 trucks that keep the familiar 3.0L Duramax inline-six, with hardware updates and a larger optional fuel tank rather than a power bump.
Dealers are expected to start receiving 2027 HD trucks in late 2026. Light-duty 1500 models arrive on a similar timeline. Pricing has not been announced yet.
Why the New Duramax Matters
Duramax has powered Chevrolet and GMC trucks since 2001. The 6.6L L5P that currently sits in Silverado HD and Sierra HD makes 470 hp and 975 lb-ft. The new 8.3L jumps those figures by 85 hp and 255 lb-ft.
GM designed the engine in-house as a clean-sheet heavy-duty V8—the first time the company has done that for an HD pickup diesel. It uses a compacted graphite iron block, forged crankshaft, forged connecting rods, and steel pistons. Cooling is handled by a dual-stage air-to-water charge cooler and a variable-geometry turbocharger built for long grade climbs and sustained towing.
Production happens at the expanded DMAX plant in Brookville, Ohio, after a $920 million investment that put machining and assembly under one roof.
The engine pairs with an Allison 10-speed automatic. RPO code is L6P, replacing the outgoing L5P.
2027 Duramax Engine Specs at a Glance
| Engine | Application | HP | Torque | Transmission | Peak advertised towing |
|---|---|---|---|---|---|
| 8.3L Duramax V8 (L6P “Mongoose”) | Silverado HD / Sierra HD | 555 | 1,230 lb-ft | Allison 10-speed | 38,000 lbs gooseneck / 20,000 lbs conventional |
| Enhanced 6.6L gas V8 (L8S) | Silverado HD / Sierra HD (standard) | 412 | 472 lb-ft | Allison 10-speed | 19,000–20,000 lbs conventional |
| 3.0L Duramax I6 (LZ0) | Silverado 1500 / Sierra 1500 | 305 | 495 lb-ft | 10-speed automatic | ~12,000–12,100 lbs |
Figures are manufacturer-claimed and configuration-dependent. Horsepower and torque use SAE J1349 testing.
Compared with rivals (latest publicly cited high-output ratings):
- Ford 6.7L Power Stroke H.O.: 500 hp / 1,200 lb-ft
- Ram 6.7L Cummins H.O.: 430 hp / 1,075 lb-ft
The new Duramax leads on both paper numbers. Ford still advertises a higher 40,000-lb gooseneck rating on some Super Duty configurations.
2027 Chevrolet Silverado HD and GMC Sierra HD: What Changes Besides the Engine
The HD trucks are a mid-cycle refresh, not a full redesign. The next all-new generation is expected around 2029. For 2027, GM focused on power, control, and towing hardware.
Towing and payload (properly equipped)
- Max gooseneck: 38,000 lbs (typically 3500 HD dually)
- Conventional: up to 20,000 lbs
- Diesel dually models: at least 30,000 lbs
- GCWR: up to 46,500 lbs
- Silverado HD max payload listed at 6,170 lbs with the diesel; gas models can go higher on payload in some configs.
GMC lists Sierra HD 2500 max available towing at 23,100 lbs and 3500 at 38,000 lbs.
Chassis and driver-control updates
- Segment-first rack-and-pinion electric power steering for HD trucks (about 30% more assist than the old hydraulic gear, less kickback, no hydraulic pump noise)
- Segment-first eBoost electronic brake-boost with 14.6-inch front rotors and four-piston calipers
- New Terrain Mode on ZR2 / AT4X: one-pedal off-road control in 4HI and 4LO
- Updated Tow/Haul, Off-Road, and Normal modes that coordinate engine, transmission, steering, and brakes
- Up to 14 camera views, Transparent Trailer View, trailer tire-pressure/temperature monitoring, and in-vehicle trailering app
Off-road trims (Silverado ZR2, Sierra AT4X) get a 1.5-inch factory lift, Multimatic DSSV dampers, 35-inch mud-terrain tires, and extra skid plating.
Trims carry over in structure: Silverado WT, Custom, LT, LTZ, ZR2, High Country; Sierra Pro, SLE, SLT, AT4, AT4X, Denali, Denali Ultimate. Denali Ultimate is shown with the 8.3L Duramax as a highlight package.
Light-Duty 2027 Silverado 1500 and Sierra 1500: The 3.0L Duramax Stays
The half-ton trucks are a new generation. Their diesel story is quieter.
The 3.0L Duramax inline-six returns at the same 305 hp and 495 lb-ft. GM did not chase a horsepower war here. Instead it updated pistons, turbo vanes, the NOx sensor, sealing, fuel-injector corrosion protection, and DEF level indicators. A larger DEF tank is also part of the package.
Towing with the 3.0L is listed around 12,000 lbs (Silverado) and 12,100 lbs (Sierra)—down from the previous generation’s advertised 13,300-lb peak. Payload is roughly 1,850–1,870 lbs. An optional ~34-gallon fuel tank is estimated at more than 900 miles of highway range.
The 3.0L remains the torque-and-efficiency play next to all-new Gen-6 Small Block V8s (5.7L at 402 hp / 428 lb-ft and 6.6L at 481 hp / 501 lb-ft) and an enhanced 2.7L TurboMax four-cylinder.
Chevrolet also made the Duramax available on Work Truck trim for the first time in the new generation, which matters for fleets.
How Chevrolet and GMC Position the Same Engine
The hardware is shared. The personality is not.
- Chevrolet Silverado HD leans work-truck and ZR2 off-road. High Country is the luxury cap.
- GMC Sierra HD leans premium: Denali / Denali Ultimate materials, massage seats, Vader Chrome, and the most aggressive trailering marketing on the 38,000-lb figure.
Both brands get the same 8.3L, the same Allison 10-speed, and the same steering/brake architecture. Buyers choosing between them are mostly choosing cabin, grille, and trim philosophy.
When You Can Order and What Is Still Unknown
- Arrival: late 2026 at U.S. dealers for both HD and 1500 trucks
- Order guides: 2027 HD fleet guides already list L8S gas and L6P Duramax
- Still unannounced: MSRP, option-package pricing, exact fuel-economy ratings, final payload charts by cab/bed/axle, and how widely the 8.3L will be available below Denali Ultimate / High Country
Expect the 8.3L to carry a sizable premium over the enhanced 6.6L gas V8, as the current 6.6L Duramax already does.
Who the New Duramax Is For
The 8.3L Mongoose is aimed at owners who tow fifth-wheels, gooseneck equipment trailers, or commercial loads day after day and want class-leading diesel output without switching brands. The 3.0L Duramax in the 1500s is still the long-range, high-torque daily driver for people who want diesel efficiency without heavy-duty size, weight, or cost.
GM’s bet is straightforward: diesel still dominates HD purchase decisions (the company says more than 60% of HD customers choose diesel), and a bigger, in-house engine plus modern steering and braking is how Chevrolet and GMC stay in that fight.
Quick FAQ
Is the 6.6L L5P Duramax gone?
Yes, in 2027 Silverado HD and Sierra HD. It is replaced by the 8.3L L6P.
Will light-duty trucks get the 8.3L?
No. The 8.3L is an HD engine. The 1500s keep the 3.0L I6.
Is “Mongoose” the official name?
It is GM’s internal nickname, used in teasers. Marketing badges say Duramax 8.3L.
When is the next full HD redesign?
Reporting points to roughly the 2029 model year.
If you are shopping 2027 Chevrolet or GMC trucks specifically for Duramax capability, the decision now splits cleanly: 3.0L for half-ton range and refinement, 8.3L for maximum HD torque and trailer ratings. Official pricing and complete towing worksheets will decide how competitive those trucks are on the lot later this year.
