Is it the transmission or the clutch?
 

My 5th gear grinds bad. I can shift gears from 1 through 4, but shifting to 5 is a pain. I have to push it in and hold it in there for the long drives. I noticed it slipped out to neutral when I was slowing down on the highway.

I know I need to get this issue fix, but what should I get to make my driving great again?

If it goes into all gears but 5th without grinding, the 5th gear synchro is done. I don't know for sure what would be the cause for popping out of gear, but it's transmission related.

If you're still driving the 240SX, which is the only car listed in your profile, you might want to check with a NISSAN forum for more specific advice.

I forgot to change that. I have a 90 gtu with this problem.

its def a technical issue with the synchros in the tranny

I was thinking about buying the tranny and not deal with having to open up the current tranny and fix it. I ask because I dont want to buy the clutch and find out that it was the tranny.

I should be all set once I get a functional s5 tranny, correct?

It sounds like a transmission issue....NOT the clutch.

Fifth gear synchronizer is prone to break i replaced mine in an hour. Not including removal of transmission. Worst part is the long bearing puller needed. Had to fabricate one. Other than that it is not hard at all. There is a writeup on here somewher that is very idiot proof.