my superduty 19- no matter what. loaded,unloaded, in wind, with a tail wind. it is a truck, it is used for towing. you have never mentioned what your mpgs are towing.
sorry. this just makes want to be you more. all you have to worry about is 6-9 more mile out of a tank of gas. 5280 ft X 6-9 and just drove that much less.