XRAY - Model racing cars

I am having a problem with the tracking and steering of my M18 Pro. It is only a few days old and has been run only a few times. The problem wasn't there right at the start of using it, but developed pretty quickly a few runs after doing the ball diff break-in.

I am running it on a carpet surface.

What is happening is that when I accelerate the rear end of the car seems to be pushing harder with one side than the other and it causes the car to accelerate turing to one side - mostly to the right. When I let off the throttle, the car still goes to the right.

I am running the all of the stock parts that came in the M18 Pro package at this time - I have not put in any of the adjustable turnbuckle parts yet.

I can sort of tweak it out by adjusting the anti-droop hex nuts, but it doesn't seeem like the right way to be handling this issue as these adjustments only seem to affect the running of the car on the specific taction that the running surface provides. If I change to a surface with more or less traction, the problem appears again.

Please help me with what adjustments I should be looking at to correct this problem.