Upgraded TT to JayFeather series ~ 5.5K lbs fully loaded. Towed from Memphis to Orlando/Disney area and back. Terrain varied but mostly had to run at 3K+ to hold 65mph on even or slight upgrades and 70 was only possible going down hill. While I don't like running the engine that high I wonder if that is within normal tolerances and especially for a 15-hour session. For a long trip, what is the upper level of RPMs for the sake of the engine and/or the transmission?