How cold is it in Boise?
You want your transmission temps to be at least 150°f for it to work properly.
As long as it does not run much over 190°f you are golden.
The first thing you must do is blow out your factory cooler in the rad both ways with air.
If you can get a baseline of trans temps first, it will help you to determine what size to get.
301-707-3437
Tom