well the reason why I spoke about the ball on the shaft, is if that shaft is spinning freely inside the worm gear, then it could sound like a bad bushing as the tollerance on the gear to the shaft is not that tight. Hence why the ball is used. Are you sure you're hearing it in only 5th gear? Is it that you're hearing it at a certain speed? So what happens if you get up to highway speeds(unless you don't think it's a good idea because of the sounds you're hearing) and put the tranny in neutral. Do you still hear the whine?

I would make sure there is proper fluid in the TC and tranny too. I hope they didn't forget to fill it all up.