GMC Sierra gains beefed up V-8s but lowers fuel economy

Auto Nov 06, 2026

The 2027 GMC Sierra is rolling out with beefed-up V-8 engines: think a new 5.7-liter V-8 with 402hp and a bigger 6.6-liter V-8 pushing 481hp.

But all that muscle comes at a cost: fuel efficiency drops to just 17 mpg and 15 mpg for these engines, which is lower than before.

Duramax diesel 25 mpg in 2WD

If saving on fuel matters to you, the diesel option is hard to beat.

The Duramax diesel engine gets a solid 25 mpg combined in two-wheel-drive trims, way ahead of the new gas models.