I'm pretty mechanically inclined, done everything but the tranny and the rear end myself. I took mine to a reputable tranny shop and got them to rebuild it.

Got around 20k miles on it and someone totaled out the Explorer for us.

As I understand it the problem is fairly typical of Ford. They love their smooth shifting transmissions so the wear and tear is greater than it would be with a moderate shift kit. There generally isn't a single component failure, it is just wear on a lot of components.