The GMC Sierra's powertrains are shared with the 2014 Chevy Silverado, and posts identical fuel economy numbers.
Those EPA figures settle in at 16 miles per gallon city, 23 miles per gallon highway, or 19 mpg combined, for trucks with the V-8 and rear-wheel drive. With four-wheel drive, the V-8 and six-speed combination nets fuel economy of 16/22 mpg, or 18 mpg combined.
Those numbers represent a significant gain over the previous GM V-8 lineup, even though the automatic transmission hasn't gone to the eight-speeds now found on the Ram 1500. GMC says it's due to more efficient body construction (the trucks weigh about as much as an Audi A8) and the use of cylinder deactivation on both the V-8 and the V-6 engines. When driving loads are lighter, the truck shuts off four cylinders on the V-8, running it on the remaining cylinders until driving demands increase. The increases in vibration and noise are offset by more sealing and on the V-6, with a balance shaft. The big V-8 also gets active noise cancellation, we've heard.
Cylinder deactivation is applied to the V-6, even, but it's not across three cylinders, just two. Those V-6 powertrains are rated at 18/24 mpg or 20 mpg combined with rear-wheel drive, or 17/22 mpg or 19 mpg combined with four-wheel drive. Those numbers are close to the ones posted by the V-6 Ram 1500, even without the Ram's eight-speed automatic.
Both engines run on regular unleaded gasoline. No plans for diesel engines have been announced, and the former Chevy Silverado mild hybrid won't be making a comeback.
No gas-mileage figures have been released for the 6.2-liter V-8. We'll update this review as soon as figures are available.