Sonic Shifter Drivetrain Problem

[jdaming]

We recently purchased the Sonic Shifter upgrade kit. We have mounted it on our kitbot and all of the pneumatic shifting seems to work fine. We have an intermittent problem with one side "sticking" a little more than the other. I know a little deviation is normal but this seems extremely excessive. The other side seems to run great. Both sides will turn and at some times it appears they are going the same speed but at other times it "sticks" and goes slower. This behavior is present in both high and low gear. Two things have me worried:

1) On the side that is affected there is a spacer that seems to be a little loose. It is still around the shaft but it can be moved unlike the other side which is solid. It doesn't seem like this would be a problem but it is the only physical difference between the two sides that I can see.

2) The side that appears to be working I can turn the wheels and when applying enough force it will turn the gears. On the other side it is quite difficult to turn the wheels by hand.