My two bits on tow/haul mode, is if the engine or transmission sounds or feels that it is shifting (down shifting or straining more often than normal with the load) to maintain speed up hill or on level road then use tow/haul mode all the time the load is pulled or in the cargo area. In the normal driving mode, As long as you don't hear the squirrels yelling Scotty's famous line "captain I'm giving her all Iv'e got; She can't take no more!" then I say don't worry about tow/haul mode. If you feel She (PM) is downshifting and straining a little more than you think then engage tow/haul mode a stay in that mode until the load has changed or the road grade is not as steep or strenuous on the system. My philosophy is to burn more fuel than to damage a motor and/or transmission.
A bit more: I have several hundred pounds of tools, and cabinets loaded in mine all the time. and have helped people move and had my cabinets and their furnishing both in the mix of weight and cargo. My PM drives fine (without strain) in normal mode. I have occasionally punched the tow/haul mode and driven in this mode just to make sure. I feel a difference in the rpm's and shift patterns; and can tell that if I had a trailer or more load it will come in handy, but I currently run in normal mode.
Hope that helps
