General Motors has released fuel economy data for the 2027 GMC Sierra 1500, highlighting performance trade-offs in its redesigned engine lineup. The new 5.7-liter V8 produces 402 horsepower, while the 6.6-liter V8 delivers 481 horsepower. Both engines are paired with a 10-speed automatic transmission.
The 5.7-liter V8 in two-wheel-drive Pro and Elevation trims achieves 15 mpg city, 19 mpg highway, and 17 mpg combined. Four-wheel-drive versions of these trims, along with the AT4 and Denali, are rated at 16 mpg city, 20 mpg highway, and 18 mpg combined.
The 6.6-liter V8 in Denali and Denali Ultimate trims returns 14 mpg city, 18 mpg highway, and 15 mpg combined. The off-road AT4X trim with the same engine is rated at 13 mpg city, 17 mpg highway, and 15 mpg combined, dropping to 14 mpg combined with mud-terrain tires.
The 3.0-liter Duramax diesel remains the most efficient option. Two-wheel-drive diesel models achieve 25 mpg combined, while four-wheel-drive versions reach 24 mpg combined. Even the diesel AT4X trim delivers 21 mpg combined, outperforming the gas-powered AT4X by 6 mpg.
The new V8 engines offer higher power output than the 5.3-liter and 6.2-liter units they replace but show lower fuel efficiency. The 2027 lineup also includes a 350-horsepower 2.7-liter TurboMax four-cylinder engine.
