Run a transmission cooler.
I know I know...you already have a cooler built into the radiator. Okay, bypass that immediately. Run a big cooler in front of the radiator. Don't worry about the openings left over in the radiator tank. Leave them open doesn't matter. If any coolant leaks out of your radiator through the cooler lines, your radiator is junk anyway.
If you are running a Centrifugal Supercharger and need the space for your FMIC then stack the transmission cooler on top.
But whatever you do, DO run an external cooler. Heat kills.
Don't believe your tranny makes heat? With the engine cold, go hold the brake and rev the engine up in Drive (to stall speed) then go grab ahold of the metal part of a transmission cooler line. After you are treated for 2nd degree burns on your hand where you grabbed it, you may note that the radiator was still cold when the cooler line was hot.
Heat kills.
Then start saving up your money for a built automatic or a manual swap, 'cause you will hand-grenade a stock auto on boost.
There's nothing wrong with an automatic per-se. Eventually those Fox-body Mustang guys lose the 5 speed and go with a C-4 automatic when they want to go REALLY fast.