[PVCMike]

It's asking a lot in my opinion to expect that they all output the exact same torques and speeds at a given current. We've run mechanum drives many times. In the past, we've used encoders, gyros and accelerometers to combat the issue of varying wheel speeds. They all proved pretty effective in measuring these variations and sorting them out electronically.

From a mechanical standpoint, I would definitely (with the robot off) give the wheels a spin with your hands to make sure the resistance is relatively the same on all 4 wheels. Also make sure all of your electrical connections are good and tight and that you're getting equal output voltage to each motor.