I have a 02 duramax crew cab short bed with K&N cold air intake, and an edge attitude power adjuster that adjust from 30-120 more Horses with another 330 lbs of foot torque and the best I ever got was 20mpg with a fourwheeler in the bed on highway driving about 70mph. That was the only time. Find myself on the gas way more puffing out black smoke with the upgrades. The best I got after that was an average of 18.5mpg on highway empty, 15mpg highway pulling 23ft enclosed aluminum trailer with 4 bikes, 1 fourwheeler, and loaded down with all the camping accesories. Get about 16.5 driving around town.