I had to haul a ton of krap to a flea market this past spring (just stuff inside, no trailer)...it was 4:30am - I was tired so I just set the cruise to 50 mph and drove like 45 miles total..got 23-25+ mpg (which I havent seen ever again since I normally drive like 85 mph

so I'd say 55 and under is best mpg as most cars....60 and over and your dipping in a few mpg's

Now have well over 18,000 miles too! Good break in I guess....