My 03 2500 quad cab 4x4 long bed 6spd ho gets a solid 20+ unloaded on the highway and 16/17mpg towing a flat bed car trailer with 4000+lbs at 65/75 mph.This is with a smarty jr set on performance setting #3. Truck has 373 gears and 1 size larger than factory equipped tires, truck has 130,000 miles on the clock.