2018 GMC Sierra C15

Truck Flex Fuel
GMC Sierra C15 2018
20MPG Combined
5 Trims
← 2017 2018
Updated February 27, 2026

The 2018 GMC Sierra C15 is a Truck that delivers 17–20 combined MPG depending on trim. Here’s everything you need to know about this vehicle, from fuel economy to safety ratings.

2018 GMC Sierra C15 Specifications

SpecValue
Combined MPG17–20 combined MPG depending on trim
City MPG18
Highway MPG24
Body StyleTruck
Fuel TypeFlex Fuel
DriveRWD
Available Trims5

Available Trims

TrimMPG (City/Hwy/Combined)EngineTransmission
Auto18/24/204.3L 6cylAutomatic 6-spd
Auto16/22/185.3L 8cylAutomatic 8-spd
Auto16/23/195.3L 8cylAutomatic 6-spd
Auto16/23/195.3L 8cylAutomatic 6-spd
Auto15/21/176.2L 8cylAutomatic 8-spd

Annual Fuel Cost

Based on EPA estimates, the 2018 GMC Sierra C15 costs approximately $2,540 per year in fuel. This assumes 15,000 miles driven annually and current fuel prices.

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