2024 Gmc Hd Duramax Fuel Mileage. For the power, comfort and capabilities, my expectations have been. Since my 2021 duramax got a new ecm flash from the dealer, it’s getting even better fuel mileage mid 20mpg canadian driven at the speed limit.

Since my 2021 duramax got a new ecm flash from the dealer, it’s getting even better fuel mileage mid 20mpg canadian driven at the speed limit. That truck is a beast.