First, check that nothing is binding in the drive system. Put him up on blocks, and run the tracks, making sure they are both the same speed. This is adjustable with the DMD system. If they are not running the same no load speed, check for binding in either side of the drive train system. If all is the same, put him on the floor, run him, and see if he runs straight and true with the steering stick in neutral. If not, follow the instructions to reset the DMD/TO system, and test again. If still pulling to one side or another, then adjust the rudder pop on the DMD/TO. If still having a problem, check wheels and idlers for a bind.
Also, are the transmissions making any unusual noises?