Every shift is one shift closer to transmission failure. Hunting is unnecessary, and frequent, shifting, which is easily controllable in most cases.
If the transmission is hunting, manually select the gear it keeps shifting down to until you get on the flat again. If it's hunting on the flat, shift down and leave it there until you get to your destination.
Tow/Haul Mode is for towing and hauling, period. If it were for descending hills, it would be Hill Descent Mode. Some Tow/Haul Modes do have a Hill Descent Mode included, but it is only part of the picture.
Use Tow/Haul or don't. You are not going to hurt a thing trying different combinations to see what works best for you.