If you just got the grind, I've seen a couple cars with 4th gear grinds be totally cured by BG Synchroshift. My VIII started this at 22k, I changed to BG, and it was butter at 53k still when I sold it. BG is really nice stuff.

Never had a 5th gear grind, but its worth trying.

 

Had my 5th replaced with cams. It's a toss-up.

 

Um. I use the same fluid, but it doesn't cure it on my transmission at all. It makes it smoother but I still have the grind from 4th to 5th (after 5k rpm).... ... Man..

 

i got used to my grind i guess...