I think the tow haul function (when to use it) is dependent on the weight and other drag of the RV.
I have 11,300 lb class C and I do not use it in general driving. The standard shift program is more suitable. IMO tow haul downshifts on decel excessively or on minor downhill grades where no downshift was necessary. The RPM will climb to 4000+ for no reason (tow haul can't anticipate the end of the hill).
Where the tow haul mode is useful to me is primarily engine braking when actually needed. Tow haul is a useful tool in the toolbox, but for general use leads to too much engine racing in my class C-a light unit on E450.