As I posted on another thread, I recently had a Quaife diff installed, which required taking the transmission apart completely, installing the diff, then putting it all back together. It took a couple of days, but having had a look inside, and a transmission expert do the work, all is well. It is a really good trannny.
So something is very wrong to need 3 transmissions, and one would hope that a Ford engineer could figure that out quite quickly. As FGIALC has opined, it's probably not the transmission, itself.
I really am truly sorry for your troubles, and do hope that Ford sorts this out as the car is a gem, and the odd (as in statistically an outlier) serious problem such as yours needs to be resolved quickly by someone who knows what to do which, sadly, is unlikely to be a Ford dealer.