How about the Damping fluid in the Shocks.
Could it have Partially leaked out of one or two shocks?

I Ran out of the Correct weight Fluid for my MXT Shocks, Had to rebuild the Front Left shock, and had to use a Lighter oil in That One Shock.
The Result was Tourque Steer, (not as Bad as Yours seems to be though).

Just a Thought....Maybe its a RADIO problem.....Have you tried swapping out the Transmitter/Receiver?
Some weird Interferance/Noise due to cable routing?