[j.cole]

Have you double checked your victors (swap em with others if possible).
Have you checked your PWM's. (swap them and make sure they are in the correct ports)
Is the wiring correct on the motors.
Like above make sure your code is designated to victors and not jags.
Try using a arcade or tank drive to see if the same thing happens (to be sure if it is a hardware issue or a code issue).
Wire constants to switches to see if it is a joystick problem.
If all that doesn't work I don't know what to tell you.