AAHHHHHH, I finally figured out how some of you get such better mileage than me. You live in the flatlands. A whole gaggle of us went down to Roebling Road this weekend and ran an event with The Dark Side. Towing 75mph, I was getting 13.1mpg... that is 1.5mpg better than I get going to VIR (with an open trailer). Why? Because it was a flat haul all the way across SC and GA. For me to go to VIR, I hit the hills of NC and VA. Not mountains, but hills and they do seem to make a difference. Running around RRR all weekend without the trailer, I got 17.3mpg... that is the best mileage I have ever seen out of my truck.
13.1mpg? Lucky... I only got 10.8mpg!