I plumbed my trans cooler into the line returning the fluid to the trans. Granted warm-up is slower, but in the hot summer, the trans fluid can still cool down before re-entering the trans.
I bought the second largest size stacked plate (better) cooler that the parts store sold. The largest one had clearance problems with the radiator support. You'll need to pull the bumper cover off to attach the cooler, but its not difficult. A tiny pipe cutter will be needed too. While you are at it, with the ATX spend some extra cash and put an inline filter on it as well.
My trans temp and my coolant temp currently stay within about 20ºF of each other under almost any driving conditions.
