Help...Robot drifts right went stopping

[eneubec1]

Hi we are a rookie team trying to trouble shoot a problem that has us perplexed.
Our robot was driving fine and then something unknown happened that is causing our robot to drift right once the motors are turned off.

Robot Drive:
We are using a 4 motor arcade style drivetrain. We have spent about 6 hrs troubleshooting this problem and still perplexed. We are a rookie team and really don't know what parts are suspect to failure, but have done a bunch of debugging. If you have any guidance, please help.

Symptom:
When the joytstick is released the right side glides to a stop and the right side comes to a prompt stop. This causes the robot to sway right when ever we stop. It almost acts like there is some very small digital "reverse" spike coming the victors and causing the motors to come to an abrupt stop.

Here is what we have done so far:
1.) Test each motor to make sure they work individually.
2.) Tore down the gearbox to make sure there wasn't anything causing it to stick.
3.) Directly powered the cims from the battery (removed the programming, victors, Crio/Sidecar, wires ) from the equation. This resulted in the wheels coasting to a stop. (they didn't abruptly stop). ---This told us the gearbox and cims were ok.
4.) Added the victors back into the equation and the problem came back. We drove those 2 victors from different PWM outputs and the problem stayed with the victors.
5.) Changed out PWM cables and experienced no change.

We are thinking one of the 2 victors is intermittently defective. Do these victors go bad?

Any advice?