My 2011 F250 has tow haul and I hate it. I just run it in D, if tranny starts shifting alot, I drop it in M 4 or 5 and run it flat out. If you have an OD option, I would not tow with it on. There ain't enough flow of oil going to the cooler, the OD clutch pack will fry even if you have an extra capacity cooler. I tried towing in OD once with one of my F150's, undercoating on the floor boards was sizzling around the tranny.
East Bound & Down- We Love Camping :)