Transmission

Have a 1988 528 with 5 speed. Was driving last week shifted to 3rd and it wasn't there and went to 4th ok downshifted and 3rd was there and then went from there it was 4th that was missing then the it would be ok for a while then it would be gone. Finally it would only go in reverse. It is like the linkage is hung up. Do I have clutch, linkage or synchronizer problems.