Greg
The trans you have is a 4R1oo ,this unit was designed by Ford to handle the excess torque of the powerstroke.
but again they forgot that when you give customers the opportunity to haul larger loads they will do it.
Slow soft shifts and convertors that have stall speeds that are to high for towing heavy loads are a ticking bomb waiting to go off.
HEAT is the KILLER.First thing, install the largest,highest flowing trans cooler you can findand install it in series with your stock cooler.
At BD here we build and sell custom built units ,designed for the customer who tows heavy,and makes the weekend run at the stripe.These trans and convertors are quarenteed to 400-450 rear wheel HP.push ,pull,or drag whatever you want.You can purchase just a convertor and accumalator valve body or go all the way to the custom built trans.
Convertors are all furnise brazed units ,that have custom stators,torrinton stly bearing and larger lockup linning surfaces.
Accumaltor valve bodies include all nessary valves and sprigs to customize shift points for your driving style.
Transmissions all have updated clutch packs and more clutchs for each gear,all aluminun sprague units are replaced with steels,and lube circuits are changed to direct lube to parts of transmission that BD feels are lacking like the overdive unit itself.We even recommend that you tow in overdrive if you have enough power to do it.
Their are many good quality transmission builders around but I feel BD has one of the best on the market and we back it up with our nation wide warranty.
If you want more technical info give me a call and I will hook you up with BD's Ford Trans specialist.