The impending arrival of the 2027 Chevrolet Silverado 1500 and its GMC Sierra fraternal twin are the biggest news at General Motors right now, but their heavy-duty siblings might steal some of the spotlight if recent reports – allegedly from within GM – are to be believed. The Silverado 2500HD and 3500HD, as well as their respective Sierra equivalents, are slated to get two new engines for the 2027 model year.
Notably, these new powertrains seemingly will arrive during the heavy-duty trucks’ current generation, rather than waiting a couple years for the redesign. That practice isn’t new at GM, and customers reap all the benefits.
The Big Trucks Will Get New Gas And Diesel V8s
2024 – 2026 GMC Sierra 2500HD 5th Gen (GMTT1XX) Facelift PickupGMC
As reported by GM Authority citing sources within the automaker, both of the engines found in the Silverado and Sierra HD will be replaced for the 2027 model year. The current 6.6-liter gasoline V8, codenamed L8S, is reportedly on the way out, with an L8T V8 of the same displacement taking its place. For 2026, the gasser produces 401 horsepower and 464 pound-feet of torque, numbers that we presume will rise in order to better compete with Ford’s 7.3-liter “Godzilla” V8 that produces 430 hp and 485 lb-ft.
Despite sharing a displacement with the sixth-generation, aluminum-block V8 found in the Silverado and Sierra 1500, we expect the L8T to retain its predecessor’s robust iron construction. As a result, it probably won’t crest the 500 hp we expect from the smaller trucks’ optional 6.6-liter V8, tuned instead for greater low-end torque and towing performance – plan on around 450 hp and 500 lb-ft for the HD gassers.
Diesel fans, don’t worry. You won’t be left out of the fun. According to an ordering guide revealed by Jones Chevrolet in Wisconsin, the 2027 Sierra and Silverado HD will also receive updates to their optional Duramax turbodiesel V8 (with a corresponding order code change from L5P to L6P in the process). The ordering guide didn’t include the oil burner’s displacement, which could mean that GM is considering upsizing its Duramax in order to match or beat the output of its competitors at Ford and Ram.
GM 6.6L Duramax Turbo Diesel Hood Badge close upChevrolet
The L5P, which first debuted in the 2017 Silverado HD and Sierra HD, hasn’t been updated much in the intervening decade. When introduced, it made 445 hp and 910 lb-ft, but in 2024, a higher-pressure fuel system boosted those numbers to 470 and 975, respectively. Still, that lags behind the Ram Heavy Duty’s 6.7-liter Cummins engine (1,075 lb-ft) and the Ford Super Duty’s 6.7-liter Power Stroke (either 1,050 or 1,200 lb-ft, depending on the state of tune). For GM to really compete in the heavy duty truck arms race, we think the L6P needs to produce at least 1,100 lb-ft of twist.
Why Is GM Reportedly Introducing These Engines Now?
Typically, automakers wait until a major redesign to introduce new powertrains. But GM has a history of updating its heavy duty trucks between generations (and even between facelifts). The aforementioned 2017 Silverado and Sierra HD received that L5P engine in 2017, three years before the trucks’ planned 2020 redesign. Why the automaker does this, no one knows, but customers won’t complain if it means they don’t have to wait for GM’s latest and greatest engine technologies.
2025 Chevrolet Silverado 2500HD ZR2 towing trailerChevrolet
Speaking of, although the redesigned, light-duty Silverado and similarly new Sierra are due later this year, their heavy-duty siblings will have to wait until 2029. In addition to revised sheetmetal and new interiors, we expect the HD trucks to also receive more towing and payload capacity, improved active safety, and more technology to help owners get work done efficiently.
Base Trim Engine
6.6L V8 ICE
Base Trim Transmission
Allison 10-speed automatic
Base Trim Drivetrain
Rear-Wheel Drive
Base Trim Horsepower
401 HP @5200 RPM
Base Trim Torque
464 lb.-ft. @ 4000 RPM
Base Trim Battery Type
Dual lead acid batteries
Infotainment & Features
8 /10
CarBuzz Insight – Why This Matters:
The 3/4-ton and 1-ton pickup segments are incredibly competitive, and GM hasn’t been able to match its competitors’ spec chart prowess for a few years now – especially on the diesel front. That could be one reason why Chevrolet and GMC are allegedly receiving the new pair of gas and diesel engines before being updated entirely for a new generation.
2024 Chevrolet SilveradoChevrolet
We hope to learn more about these two new powertrains soon, but it looks like all systems are go for the 2027 Chevrolet Silverado HD and GMC Sierra HD.
Source: Jones Chevrolet on Facebook, GM Authority via Motor1
