Transmission coolers

[snowbunny]

We've been discussing this as an aside on another thread but something happened today to make me want to focus on this. I wanted to add a second transmission cooler as on my one trip towing my Montana my transmission temp was running between 190 and 210. Some of you have said that transmissions last longer if kept around 160 to 180 and that you had accomplished this by adding a second cooler. I asked my garage to install one for me and they called the Chev dealer toask him a question about the coolers. He told them that installing another cooler would void the 100,000mile warranty on my drivetrain! Obviously, I told my garage to hold off on the cooler. Also, the Chev guy said that it was normal to run at about 200 degrees. One of their concerns was that in this climate in winter (Vermont) the second cooler would keep the transmission from ever warming up at all!
Any comments?

Jim & Diane McGill
Chev 2500HD D/A 4x4 Ext Cab
Montana 3350RS
Reese 16k slider, Prodigy