2024 Fuel Mileage 6.6 Duramax Diesel. For those wondering about fuel mileage, if i spend another $100 per month on fuel, which i don't.it. 403 in 3, 6599 cm 3 power:

The engine has been updated with the latest fuel injection, combustion,. Over the full 1,563 miles, the truck reported 21.3 mpg at an average speed of 68.3 mph—while my math showed about half a mile per gallon less.