Transmission problems NB?
 

Whenever I'm in 4th gear as I accelerate then let go of the gas there a grind noise. Can it be a shot out bearing? Or something worst?

More info.
5 speed or 6 speed?
Have you kept up on maintenance?

I bought it back in October.. And the car was over heated so it sat in the shop for two months.. Had to rebuild the whole head but it wasn't too bad. Other then new trans fluid with a new clutch with fly wheel.. I don't have much knowledge on transmission maintenance. And it's a 5 speed. Also when I was stuck in traffic the other day when I threw it in neutral the rpm was at 2k when I put it in neutral to cruise with the A/C on and it goes down to 1k when I turned the A/C off is there a reason behind that?

Two different issues you've got there. You may need to clean your IAC motor to correct the idle issue.

My 5 speed does same thing in 4th, its been doing it for years with no breakage and I routinely do 4th gear roll ons with 15psi. I think there is a write up on it on m.net?