Our 2005F350 dualie had tow haul mode switch. Empty coming down a wet hill, I put it in tow hall and the truck went sideways. They changed the programming after that. Drive it in tow haul from the start won't cause any problems.
Tow Haul effectively gave to other gears. I don't remember between which gears, when not in tow haul. Probably a lower first gear and lower gear between 2 and 3. In a diesel that was lot more engine breaking, plus it engaged the engine brake....the reason my truck went sideways when suddenly engaged.
I didn't read all the replies so my apologies if someone else gave the same info.