Maybe try a full system flush (NOT just a drain and refill)?
I have also never had problems with the factory radiator, but I do plan on getting the Mountune, or Pro Alloy soon.
BTW; It amazes me just how hot it can get up there, even where one would think it has to be cooler, just due to the parallel/latitude.
I have seen/experienced over 100*F temps in northwestern Maine while working NEFR in the middle of the mountains of the 7 Islands forest, in late July!