So I've asked this question a few times. I was in the mountains in February, and it was -20F and the tranny, while pulling a trailer with 4 mountain snowmobiles on it (500# each - probably 1.5 tons total weight with trailer) and I was running trans temps as hot as 225-230F. Much too hot in my opinion, but when I talked to the dealer, they *claim* that this is normal and that it could go as high as 250F.
In my racing experience, anything under 200F is good, anything over 210F is bad, so it concerns me when it hits 225F and I can *smell* it!
Jay