okay i have a 91' ls with the 5spd in it and the other day i noticed that it started to grind every time i would go into 5th only happens in 5th but its not a grind you can hear i can just feel it through my stick and it also only happens when im going fast maybe 75+ it will do it so i was thinking of some ways to try to resolve the problem and only thought of changing the Gear Oil and seeing if that makes any difference if not i guess i will have to do something soon about it