I reviewed all the manuals that came with my TT and was unable to locate any information on what pressure I should use in the tires. I was very surprised that 5 psi would make that much difference in MPG. I know it's really very difficult to establish MPG performance due to one variable such as this. Other factors could be temperature, moisture content of the air, gasoline quality, etc, etc. But the TT tire pressue was the only thing that I know was changed. It didn't seem like I was going downhill both ways, especially on that 10 mile grade back up I-10 out of Indio. Going both ways, I don't think I went over 2500 RPM very often on the down shifts. Only when passing. According to my GPS, my maximum speed was 68.2 mph and my average moving speed was something around 52 mph. I just love the statistics you get from the GPS.