GM's V8 SUVs Stuck at 17 MPG Combined Since 2010

For a segment that has absorbed cylinder deactivation, direct injection, 10-speed transmissions, and aggressive aero refinement in the intervening years, standing still on the window sticker is a genuinely odd outcome.

The 17 mpg number applies across the Tahoe, Suburban, and Yukon, and the engine behind it is the 5.3-liter small-block V8, still GM's most efficient gasoline option in the full-size body-on-frame lineup. The arc between then and now isn't a flat line so much as a hill that climbed and then slid right back down.

GM's full-size SUVs actually reached 19 mpg combined between 2016 and 2018, a legitimate high-water mark. From 2019 through 2021 they settled at 18 mpg combined. And then, after 2021, the figure dropped to 17 mpg and has not budged since. So the net result over fifteen-odd years is a round trip: up two, back down two, and you're staring at the same number you started with.

GM's own full-size pickups, sharing much of the same mechanical DNA, improved from 18 mpg to 20 mpg between 2010 and 2025. That's roughly an 11% bump, and it wasn't magic. The gains came from base models fitted with smaller engines, which the trucks offer in a way the V8-heavy SUV lineup largely doesn't.

A fresh V8 engine family is expected to arrive in GM's SUVs, and it carries GM's sixth-generation small-block architecture. GM claims they'll deliver improved power, torque, and efficiency across the board.

The two designations to know are the L76 5.7-liter and the L78 6.6-liter. Both mark GM's comeback to the 350- and 400-cube classes, and both grew their displacement through stroke: the L76 went from 5.3 to 5.7 liters by adding 6 mm of stroke, while the L78 climbed from 6.2 to 6.6 liters the same way. On output, GM says the L78 makes 481 horsepower and 501 lb-ft, and the L76 produces 402 horsepower and 428 lb-ft. GM positions these as on par with the small-block V8s in the 2027 Corvette lineup.

If gasoline isn't your preference, the diesel path is still open. GM says the updated 3.0-liter Turbo-Diesel Duramax adds 40 horsepower and 25 lb-ft of torque over its predecessor, now rated at 305 horsepower and 496 lb-ft. Paired with that 34-gallon tank, the diesel is good for up to 900 miles of range. The catch is at the pump: with current diesel prices, the math on cost-per-mile doesn't favor diesel over the gasoline V8.

Become an AutoGuide insider. Get the latest from the automotive world first by subscribing to our newsletterhere.