all the time i step on my car and changing gears at high revs my third gear barely grinds but all of the other gears go in fine its just 3 and when i drive normal the gear goes in perfect with no grind its only when i step on it could it be probalbly the oil i put in it and i have to put in better oil i put 10w-30 penzoil

 

sounds like ur synchro is going out in third. adding more oil will help only if ur low.
im not sure about adding thicker oil. it might. ive never done it tho

 

but thats weird how come it only grinds at high revs and when drinving normal it doesnt grind not even close to grinding it shifts like a normal car wouldnt it grind to when driving normal if it were a synchro

 

not necessarily

My Si tranny did that as well.

 

my y1 trans does the same exact thing...Im gonna try gm syncrho mesh and hope that works if not...ill drive it till it breaks then figure things out

 

Mine does the exact same thing too. Only in 3rd while driving hard. That nasty loud grind. I will do a tranny flush and GM syncromesh and see if it fixes it too.