I saw what seems to be an addon trans fluid diverter valve at pnp. It's a rectangular little piece that fits between the radiator fitting for the upper line, and the line itself. Out the bottom are two stainless lines that run from/to a small cooler located in front of the main radiator. It seems this simply diverts fluid to the extra cooler, then back to the radiator, and the fluid flows through that, and then back to the trans. It seemed fairly nicely done.
I'm looking for comments about its worth, as I sometimes pull a small trailer.