the reason why I might switch is that I am noticing that the RP75w-90 needs time to heat up before the tranny will shift smoothly, and find that the fluid doesn't last well beyond 8k miles. That's when some of the notchiness of the tranny returns, and lets me know I need a change.

I live in south fl, where its hot and humid, and tranny fluid is put to the test of being heated more by the enviroment, and the possibility that moisture might be within the oil from the humid air.