2018 GMC Sierra K15

Truck Flex Fuel
GMC Sierra K15 2018
19MPG Combined
5 Trims
← 2017 2018
Updated February 27, 2026

The 2018 GMC Sierra K15 Truck provides 17–19 combined MPG depending on trim. We’ve compiled EPA fuel economy data, NHTSA safety ratings, and recall history so you can make an informed decision.

2018 GMC Sierra K15 Specifications

SpecValue
Combined MPG17–19 combined MPG depending on trim
City MPG17
Highway MPG22
Body StyleTruck
Fuel TypeFlex Fuel
Drive4WD
Available Trims5

Available Trims

TrimMPG (City/Hwy/Combined)EngineTransmission
Auto17/22/194.3L 6cylAutomatic 6-spd
Auto15/20/176.2L 8cylAutomatic 8-spd
Auto15/20/175.3L 8cylAutomatic 8-spd
Auto16/22/185.3L 8cylAutomatic 6-spd
Auto16/22/185.3L 8cylAutomatic 6-spd

Annual Fuel Cost

Based on EPA estimates, the 2018 GMC Sierra K15 costs approximately $2,650 per year in fuel. This assumes 15,000 miles driven annually and current fuel prices.

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