I knew I wanted to keep the 4L65e cooled as efficiently as possible but I also wanted to keep the cooler out of the radiator and away from rock strikes etc. I ended up putting it in the engine bay on the fender and swiss cheesing the wheel liner to get the puller fans to draw cool air through the heat sink.
While this worked ok for a while, when I started towing the trailer I ran into cooling issues. The trans would get really hot and stay hot. Long grades were tough on it. I decided to run the lines through the radiator and then into the cooler. I am happy to report this has been very successful. Took a drive today up my local grade (about 2000 feet in about 3 miles) and while it got hot, it was about 30 degrees cooler than before and interestingly the trans body stayed cooler than the pan which tells me the cooling is working.
As you can see I run two trans temp sensors. One is in the body in the stock location and one is in the pan in the MagHytec pan I have. I can swap between them using the switch and also the LED underneath the switch comes on when the trans cooler fans kick in at 180 degrees.
I swapped out to the Amsoil ATF fluid and these are the results. First is the trans body temp, then the trans pan temp, then engine temp