Fuel Economy varies on 3.0L Duramax equipped vehicles. 2020-2021 2WD Silverado 1500 trucks get 23 miles per gallon in the city and 33 miles per gallon on the highway. 2020-2021 GMC Sierra 1500 trucks with the 3.0L Duramax get 23 mpg in the city and 30 mpg on the highway. Full-Size SUVs with the 3.0L Duramax vary between model with the best being 2021 Chevy Tahoes getting 21 mpg in the city and 28 mpg on the highway.