Originally Posted by bchauler
Just my thoughts: Not sure if you have a cooling issue or not, but towing up very steep grades is the hardest scenario for cooling. Engine is working its hardest and the low speeds of steep grade climbing pull the least amount of cool outside air through the rad. Instead of air pushing through the rad, the clutch fan is having to pull that air through. I would be inclined to say that everything is okay if you aren't experiencing issues in other towing situations.
^ This. Low speed, high load, high ambient temperatures all add up to higher temperatures.
Keeping it in a lower gear in order to have the revs up a bit will help the cooling.