[Jeffrafa]

Unrelated, but something else to note is R67B & R76 - I don't see a pressure relief valve connected to the compressor.

For testing drivetrain, I would recommend similar to one of Dale's suggestions - electrically disconnect the motors and test one at a time, making note that speed/direction is consistent, and listening for any unusual noises.

For PWM I also suggest to CAL the controllers together, but I don't think this is a problem over CAN. I would check that the 2 talon's status lights have the same color/blink rate throughout the output range, as a sanity check that they are being commanded with the same output.

Most mechanical issues can be heard, or felt by turning the wheels manually. With the motors electrically disconnected, the two sides should be relatively easy to back-drive on blocks, and should feel/sound consistent, no periodic difficult spots.