I am putting together an rc10l4o and after assembling the diffs have found a gritty feel. odd thing though is that I got 8 diff balls, and a kimbrough diff that has 12 outside holes and 6 inside holes. The diff is dead clean and greased perfect, can I have gotten the wrong size diff balls? maybe the wrong wrong diff? If anyone knows anything about this please let me know.

Try changing the outside bearing in the diff hub(the one that the diff nut tightens on). This bearing is normally the cause of a gritty diff that is newly built. I try to use the best bearing of the batch here.

Also , if you over tightened the diff to begin with....you may have flat spotted the stock diff balls.

and whatever row of holes you use( 12 or 6) make sure you diff balls in each hole.