Transmission Failing

[EddieBauer2002]

I've been having an on going issue when going into reverse in my 2002 Explorer Eddie Bauer 4WD V8. A couple months ago I notice a loud "thunk" when placing the tranny into reverse, I took it to a transmission shop and guy said it runs great. Now it has progress to when I place the tranny into reverse it's like I put the truck into neutral. Truck does not move, no indication that I placed it into reverse aside from the column shifter and the gauge cluster showing reverse. I placed it back into park and back into reverse, same issue. So I placed my foot on the gas to see if the engine would rev just as it does in neutral, then came the loud bang and the truck began to move just as normal in reverse. I was told by someone that had a 02' that my transmission is on the way out and I could have up to three months before it fails completely. Anyone else run into this issue? Anything I can do besides a complete rebuild or buying a new transmission? Thanks.