I just took a trip on my TCH. I went from Nashville to Memphis w/ AC on, cruise set usually at about 73-75. The trip is about 400 miles roudtrip w/ 95% interstate miles and my mileage was 41.7 mpg.

On my first tank I got 36.5 w/ mainly short distance driving. So in my short experience my highway mileage is much better than stop and go driving. Even on my first tank, the times I went on the interstate I almost always pegged the eco gauge at above 40mpg as well.