Do you have your gear boxes aligned so that when the bot is going forward, both motors are going in their forward direction? Or is one going forward and the other in reverse? If this is the case, that would explain the lag between the two wheels. These motors are more efficient when run in the forward direction, so if one runs opposite the other it will do so unevenly.
I will make sure to check up on this when I get to the robot. We will check once more on the driving and then I will see about this, I hope it’s not too hard of a fix… 
Our 2001 drill motors would smoke quickly whenever we stalled them (like driving into a wall, and maintaining full power to the motors). The 2004 motors are different, but I suspect they would do the same.