input gears are fine on mine, they're so small that it would be a big error in them to notice a wobble. Try going around checking the alignment of everything. Screw the top deck down before you tighten the bulkhead screws on the bottom of the chassis. I got quite a bit of spur gear wobble the first time I built my cuda, the spur was overtightened and doing as Steve said about tightening the top deck first made the spur a lot better.