If you have the stock pcm fan programming. Your fans don't come on until around 216F low speed and 228F for high speed. so unless you are moving, expect temps to rise. The transmission cooler is in the radiator... keep that in mind.
FWIW I did two 8 hour runs in 90-95 degree heat the past week, through the hills of PA and they have some hills. The first leg was actually 85-90F outside and the trans averaged 190F with a 195F t stat. On the way back temps outside were 90-95F and the trans averaged 200F with one spike to 215F. 160F is considered the bottom of the operating temps for the trans. The high end is up around 230F.
Ooooo lookey what I found
Trasmision Automatic A Buick-Oldmobile 4T65E
