I also recently seen a thread where the guy took his tranny cooler and mounted it up under in the spare tire area ( he made his own bracketry to support it).....he then mounted a small electric fan to it (just like you would see cooling a radiator but smaller) and ran power to a key on hot.....so not matter what ....rather sitting still or doing 100mph ,as long as his ignition was on his tranny fluid was staying cooled by that fan.
Just a nifty idea i thought I would mention.
I personally am going to stick with mounting in front of the radiator though.