I got a really good deal on a B&M Supercooler one a few years back from a friend. Easy install. Any
tranny cooler will help, but the stacked-plate type are most efficient (and most expensive). All I did was use a tubing cutter to remove a small section of the top steel transmission cooler line. I have the hot fluid coming out of the
tranny into the Supercooler then looping back into the stock radiator cooler and back to the transmission. I did it this way because the Supercooler actually cools the transmission too much so I have to add a little heat back into the fluid so the transmission shifts normally in the winter time.