I having recurring problems with rebuilt transmission/valve body.

What is your question?

I was feeling a vibration around 40mph. Ended up having my transmission rebuilt after 287K miles, which involved replacing the valve body with a rebuilt one. After driving for about 2 weeks I started having problems getting into gear. Took it back, they replaced the valve body again, half way home same problem again. Took it back again, replaced valve body, after driving a couple days same problems, took it back and they replaced valve body again. After driving a couple days, same thing, this time they replaced with a valve body from Ford. After driving for a couple of days the vehicle dropped out of gear while driving and would not go into gear at all. Mechanic is now starting over again an pulling transmission. Any ideas what is going on?