Overheating in NW Mountains

The critical symptoms are low power and excess heat production. This time of year, you should barely hit a high enough temp to have the fan kick in at all.

Definitely check the charge air cooler for leaks.
Also, clean out the outside of the rad, especially in between the rad and the air conditioning radiator. I had one truck that filled up with cottonwood wool, and it was like a snow storm when they blew it out from the back side with compressed air. Pressure washing from the front is not always the right thing.

But the lack of power is what concerns me most. I’ve never had to go to low range on those hills, even at 88K.