I'm sure you guys have either used Redline or Royal Purple in the transmission fluid. But if you're still having the dreaded 5th gear grind, try replacing the shifter bushings with either new ones or the solid bronze bushings. And also replace the shifter support bracket.
I replaced my shifter bushings with the bronze solid ones and also replaced the shifter support bracket and no more 5th gear grind.
Hopefully that works for you !
Follow Ups
FYI for those who are still having the 5th gear grind - Nitehawk11:12:47 04/17/13