Cougar that pulls to left on power

[martgifford]

I have a Cougar the pulls to the left when on power. It did it at the track and also when testing at home. I have measured every tie rod and shocks have been rebuilt. It's not weight either as the esc is on the right of the car which is heaver then the rx. As I have worked out its when it accelerates it is possible to be the diff? Is this a natural tendency? I think thats all that's left. As driving slow in is fine. It's something to do with the transmission it think

Can anyone help

Thanks