No reverse

Dear sirs
when I put the gear handle reverse shift it is not moving it seems the reverse shift is not working but when I shift the gear handle to the drive it is moving smoothly. I change the gear box 3 times and the same problem, After that I was confusing (all the three gears box I had changed are the same problem ) in drive is working but reverse is stopped.

Please advice

Removed engine to replace leaking seals (cam, oil pan gasket, front) put engine back put in reverse, drive and nothing. Removed engine to replace leaking seals (cam, oil pan gasket, front) put engine back in and put in reverse to back out of the garage and nothing it wont go put it in drive and it wont go. Checked neutral safety and its right. When shifted into gear the idle changes like its supposed to. Thought it was maybe the torque converter so bought a new one put it in and still the same. PLEASE HELP. I have no idea what happened. Everything worked when I pulled it in the garage. The fluid is old but full

I have a 1992 Camry, 4Cyl auto. The transmission works fine in forward gears. In reverse the transmission engages but it slips a little (still able to back up the car without excessive revs). I suppose if I were trying to backup a steep hill, I would not make it.

Might this be a minor problem or amI looking a overhaul/replacement?

Thanks.