This sounds like problem with valve body... I am assuming he is talking
about automatic transmission. If so, I would recommend they swap out the
valve body and negotiate with the dealer that it was under complaint many
time that they didn't fix it. They should cover for the majority of the cost
if not all. Get regional service rep involved.
They have STAR diagnostic machine that can test each gear independently to
determine what might cause the problem. I think something is wrong with the
electronic selenoid that operates the gearing selection on the valve body.