SR trans not shifting

[supergl74]

Well I was driving in traffic today in 5th gear, like normal, not abusing it or anything. I try to down shift to slow down but all it will do is go into neutral and back into 5th. When in neutral it works fine. But it will only stay right under 5th, it will not move side to side. And I can also put it back in 5th and it responds properly. So I removed the shifter to see if I could see anything binding on the linkage. I didn't see anything that looked odd. I have tried moving the shifter both while the engine is running and while it is off. Just feels like something is binding. Any ideas?

[Hijacker]

On the side of the trans is a plug you can remove to check to see if the retainer plunger for the shifter is working properly. I have it labelled in the above picture as Return Spring Plug. Be careful when you remove it as it does have a spring behind it and you don't want things taking off on you.

After that, my only other ideas are internal issues. Primarily bad shaft bearings come to mind. Or possibly something with the 3rd/4th shifter fork.