I have an '03 with the 4.6. I pull a 2500 lb. trailer. I know that you are supposed to dis-engage the overdrive when pulling a trailer...but what about pulling it across the flat parts of Texas where I live? I have put my truck in overdrive on some of these long stretches of nothing and it won't down shift and the revs stay the same. Am i hurting my tranny? When the terrain changes to more "hilly" roads I take off the overdrive. Is it just the constant shifting up and down that should be avoided or will just towing the weight of a trailer in overdrive hurt it?

 

Tow in any gear that will pull without hunting. If the transmission downshifts and upshifts at short intervals you are in too high a gear. Then manually downshift.