Xray 808e

[JUS4SHO]

just finished build two xray 808E with the active front diff for a friend and i we are using the castle mamba monster and the castle 2200kv motor
they were build exactly to match the manufactures instructions the problem we are having is that down the stright the rear is very loose " the rear of the buggy is like a fish tail back and forth" and we are constantly fighting to keep it stright , we have tried many different tyres same effect. We are also having a simmilar issue with the x-ray xt8 converted to electric using the rc-monster kit
can you guys give us a few ideas on what to try to help resolve this issue