We tow our 8500~lb 5th wheel all over the southeast with our 5.4L F250. It's about to be subject to towing a 7500~ lb TT in about three weeks. It downshifts on every incline from O/D at 1900~rpm to direct at 2600rpm and on the steeper inclines to 3rd at 4200~rpm. perfectly normal operation and the F250 is a solid platform to tow with within it's rated capacities. We average 8.5mpg towing 65~mph. I'm happy as a puppy with two tails with it. That said, most people throw a good ol' toddler crying fit at the first hint of a downshift, get a migraine and spend $8k+ on a diesel option to solve a non-issue. A 3/4 ton gasser will do the job well but they'll all downshift to keep the engine in it's powerband. If you're ok with that, GM, Ford and Chrapsler all make good trucks. :B
