I live in colorado. A 2000 -3000 ft climb in elevation is pretty common. I have about 140,000 miles. I’ve flushed my transmission twice so far during the life of the vehicle, last was about 30,000 miles ago. My transmission temp creeps up to about 225 on those climbs when towing about 3500lbs or over. I have a transmission cooler. Is that temperature normal? If so, what temp would be to high?
Here’s a guide for tranny temps. http://www.txchange.com/heatchrt.htm
Tester
@Dippel you have a factory transmission cooler built into the radiator, I believe.
Nevertheless, you could probably benefit from an additional, supplemental transmission cooler mounted in front of the condenser. This would have to be teed into the system, but it’s not a big deal.
It would be good if you frequently checked the transmission fluid and got a feel for any change in color. I hope by flush you mean change of fluid. If the fluid turns brownish or begins to smell differently, especially after a tow, it’s time to change regardless of miles. IMHO, when towing, that should be as much a deciding factor when to change. You may need to do it more often.