I'm a big believer in built transmissions, but have no Ford experience on this subject. I have to think there are distinct power limits on each model, but the aftermarket, assuming you can find someone that can really, no, I mean really, really build a transmission, you may never know.
Good luck in finding someone that first, is honest, then second, has integrity, then third, the expertise to combine all three of these together at the same time.
The honest guy will tell you he doesn't have the expertise, but might be able to direct you somewhere that has done some for him.
The one with integrity will tell you that he can replace it with a factory rebuild, if there is such a thing, or a new one, both sourced from Ford.
The third will have the expertise to rebuild AND upgrade the rebuild where needed. He can also let you sit and watch the process such that you will never get in trouble trying it yourself. There are lots of odds and ends to upgrades that include slight adjustments internally, to changing out factory parts to heavy duty parts. Most of these guys that "upgrade" maybe can disassemble a transmission and put it back together, maybe change gaskets that need changing, maybe improve a valve body by changing a hole size, but don't have the honesty and integrity/knowledge to do it all properly.
I have written those checks before, so I am qualified to speak. The gentleman that did my GM work unfortunately died. His work, however, still lives on.
My Fords? Never had a problem, but never messed with them either. I have owned 7 or 8 over the years, including four F150's.
