I had a 2006 V6 Toyota 4Runner that I would tow the max tow rating of 5,000 lbs during the hot summer months and wondered the same thing so I did a UOA of the oil I normally used She'll Formula Full Synthetic 5w30 and ran it for 8,000 miles and it was a great report. I then ran the same oil for the same millage during the summer months with lots of hard towing and that summer it was HOT! And I really worked this truck wide open up real long hills in third gear I expected the UOA to show elevated everything and a big drop in TBN but I was wrong this UOA was better then the UOA without towing! I was shocked to say the leased. Do a UOA and see what you get... By the way I ran a rather large aftermarket trans cooler on this truck and never had a trans issue in over 180,000 miles.