[BenI]

I've had this happen to my 5th gear-only would stay in gear if I held the lever. The culprit was a loose cone set screw in the linkage. There are two of these-one by the firewall and one by the transmission, and both are behind plastic/rubber covers. I'd inspect the linkage first, and make sure these haven't shaken loose. If they look bunged up at all, Pelican carries the part for cheap. Good luck!