46t Kyosho spur on rc8t problems?...need help from pro!

[plettenbergs]

i have the rc8t with rcm complete e-conversion...it ran kind of slow with stock steel spur gear so i switched to 46 tooth Kyosho...this is my first center diff truggy...i installed gear without rubber seal and shims the first time...before i ran it i noticed the shimms laying on the table and apon looking closer noticed the black rubber washer thingy...so i took it all apart agian and installed the rubber thing and one shim...i tested it on the deck and heard slipping...so i took it apart again and installed second shim...i ran the truck for about 10 minutes on 5s 18.5v and NOW the diff seems to be gone!!!

do i need new diff?
do i need new spur?
do i change internal gears?
i have several new UE diffs,should i upgrade?
should i put the stock spur back on?