The 2027 GMC Sierra Somehow Gets Worse MPG Than Last Year's Model

It's unfortunate that the 2027 GMC Sierra full-size pickup gets fewer MPG than the 2026 version. However, there's a simple reason for this, which for some owners could possibly compensate for the slight drop in fuel economy when comparing the two. Our introduction to the 2027 GMC Sierra revealed that it came with two new engine options.

This is precisely why the 2027 GMC Sierra gets lower fuel efficiency ratings than the 2026 model — its engines are larger, which typically means that they consume more fuel. The standard engine on most 2027 GMC Sierras is a 5.7-liter V8, which is larger than the 5.3-liter V8 that came in the GMC Sierra in 2026. While this new, larger engine boosts its power output to 402 horsepower from the previous engine's 355 horses, it does come at the cost of a bit of lost fuel mileage. EPA-estimated fuel economy for the 2027 GMC Sierra 2WD comes to 15 MPG city and 19 MPG highway, compared to the 2026's 16 MPG city and 21 MPG highway. 

This is also true for the larger V8, which is standard on the 2027 Denali Ultimate and optional on some higher trim levels. For 2027, a 6.6-liter V8 replaces the 6.2-liter that was available on 2026 Sierras. Just as with the smaller V8, the larger one has more power and gives up some MPG. The EPA-estimated fuel economy for the 2027 GMC Sierra 4WD comes to 14 MPG city and 18 MPG highway, compared to the 2026's 15 MPG city and 19 MPG highway.

The exterior design of the GMC Sierra for 2027 is all new, with a more upright appearance, a grille that's more vertical, and headlights that take the shape of the number seven. Inside, some trims come with either real wood or carbon fiber trim, panoramic sunroof, and ambient lighting. There is also a lot of cool tech inside GMC's 2027 Sierra.

In addition to the two gasoline-powered V8s mentioned above, there are two additional engine options available in the 2027 GMC Sierra. One's a base engine: a 2.7-liter inline four with a turbo that makes 350 horsepower. The other is a 3.0-liter turbodiesel that produces 305 horsepower. All Sierra engines are mated to a 10-speed automatic transmission that drives either the rear wheels or all four when equipped with 4WD. Pricing for the 2027 GMC Sierra starts at $42,095 including destination for the regular cab Pro 2WD trim and tops out at $86,480 before options for the Denali Ultimate crew cab short bed 4WD.

For most users of the 2027 GMC Sierra pickup truck, a penalty of one or two MPG is likely a small price to pay for the added performance they will receive from both of the larger-displacement V8 engines. For those who are more concerned with fuel economy than performance, there is always the choice of the turbodiesel engine, which gets EPA-estimated fuel economy of 22 MPG city and 27 MPG highway in 2WD form. For those in search of a used Sierra, we have reviewed the most reliable GMC Sierra years, and some to avoid.