I have 15' 5.7l. I haul cars to the drag strip a couple times a year. Now that the major highways where I live are 70mph now. The trailer plus car I haul I would safely say around 5k pound total. I'm new to towing as this is my first truck so forgive me if I did/say something dumb. I would put the truck in cruise at 75mph but then when any slight incline on the road the truck would shift into overdrive or down shift don't know the differnce. Even at 70mph it does it also. But if I go 65mph it barley does it. Question is am I hurting the truck but doing so?