RCM motor mount X1CRT

the center diff on my rcm x1crt seems to have alot of fore and aft movement.I did put three diff shims under the front bearing but it didnt seem to help. I have a rather anoying on and off trottle click/clack. the diffs are fresh rebuilbs,the gear lash/mesh seems good.the hole diff moves fore and aft about 1/16 with the three shims installed on the one end.any idea's?