Just so you are aware Tow/haul not being selected won't harm the transmission in the truck at all. Tow/Haul causes more favorable transmission behavior (later upshifts / earlier downshifts) but doesn't make the transmission any more resistant to the effects of towing.

 

OK, thanks, but Im not sure I believe that. Tow/haul changes the lockup RPM, does it not? Then chances are it will affect life and temp of the torque converter. But your point is well made....next time I'm towing heavy, I will attempt to watch the trans temp with and without tow/haul selected and see if I can discern any difference.