I have a 2016 ram 3500 dually, 6.7 diesel. I tow a 12x6 enclosed for the bikes. Going to Pitt I averaged 14mpg and that was 75-80mph the whole way. If I just cruise around 65mph I may get 15.5mpg. That is towing a loaded small trailer, but when I have to tow my big work trailers, sometimes 25k...