my 3rd gear grinds when either i shft from 2nd or down shift from 4th but only at 3500rpms or more..if its under then its just find..........and a few buddys told me its the synchronizers..........so do i gota buy new synchronizers.....if so how much are they if not......is there a something i can do to fix it besides taking it to a shop and everything else........cause i dont wanna make it to where ill needa new cluth caue of the grinding and ****.......please assist anyway possible...thanks

at least you isolated the problem...
is it a 5 speed?
if it is then you just need a new blocker ring cuz the synchro hub isnt locking into the blocker ring...either bad clutching teeth on the blocker ring or the hub is messed up
you defintly wont need a new clutch because all your gears would be grinding if you needed a new clutch considering the clutch effects all gears...
its most likely a blocker ring
dont worry aobut the clutch tho

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Joe