[DjScribbles]

Using feedback is the best way to go, but the following can help if that is outside your teams capabilities:

You might try using a split-PWM cable (one PWM output driving both motor controllers, with the output of one of the motor controllers reversed if needed); this would rule out any software/timing issues.

You should also try calibrating your motor controllers, to rule out the possibility of variation in the calibration causing problems.

Also, the motor controllers absolutely have to be of the same type (i.e. two talons, two victors888s, or two jaguars)