Thats great, 15-18 is reasenable. Depending on the speeds, terrain, and gearing. Hauling my 2800 lb camper, i can get 17.5 going to Missoula MT down 200 via the Kootenay National Park from Bonners Ferry. Did that a few years back. Feathering the peddle as i wasnt in a rush. Sure beat my friend Skeeter coming into Missoula from Sokane pulling a 26 footer, with a 351M, automatic getting 12. MPG