i have a wierd problem with my new transmission. i JUST rebuilt it, everything is brand new and all clearances are perfect.

for the first 50miles it worked flawlessly. but now if im like racing and the rpms are up there it will grind going into every single gear. if im just driving around normally and shifting at 3000-4000rpms its perfectly fine, no grinding. only when im revving it all the way out..and i will still shift it really slowly and it will still grind. even if i go up to 8500rpms in 2nd and then push the clutch in and hold it for a few and then shift it grinds.

i dont get it, what could be going on here?