I had to drive to my Aunt's memorial service the other day and the transmission temp never got about 160, at least not on the freeway. So I don't think disconnecting the transmission from the radiator will be any benefit to the overall cooling of the engine.

I'm going to hook up the 13k BTU aux cooler though and see if I can drop the temp on the transmission a bit. It does get up to 220 when idle after everything is heated up (at least during the summer).