I have a 1989 with the getrag 5 speed. The transmission is stuck in 5th, I believe. I can't get it out of that gear. About five years ago the same thing happened, my neighbor came over and said he knew what the problem was. He pulled the shifter out of the top of the transmission and with a pry bar, moved something in the top of transmission where the shifter normally goes and it has worked fine ever since. Until today.

What is the problem???

 

I guess the shift forks could be worn and allowing it to try to be in 2 gears at once. That is what happens sometimes to the big trucks at work.

 

I've never had this problem, but I've had my getrag apart and I think I understand what happened. I'd do the same thing your neighbor did. pull the boots off the shifter, then to pull the shifter out you need to push down on it and remove the snap ring that hold it in place. Once you get it out you will see three shift forks and the one to the drivers side (5th/R) will not be in line with the other two. To get the trans out of fifth you need to pry on that shift fork until it pops back in line with the other two. If this problem keeps happening I'd say something, either the shift forks, or the rails, or shifter pins, or the shifter itself is worn and locking up.