Skimming 8T 1.0 rear gearbox

[medusa'd maxx]

Sorry about the skimming - got to stop posting at 3 am
in response to above
Its an 8T 1.0 with a tekno conversion, Medusa 36 80 2000kv on 5s geared 13 X 48

I have the Alu Inserts
I have two shims (all I could fit) on the ring gear side of the diff
no shims on the pinion
It skips only when I mash the throttle

I'm wondering if the motors flexing the diff case
Or should I try shimming the pinion