Well I know this probably isn't it but make sure you had your slipper tightened down. I know I have forgotten to do that once. Also check and make sure that the pins are not are not sheared off on a couple of the shafts in the tranny. Only other thing I cant think of right now is possible bad One Way Hub.....
http://www2.towerhobbies.com/cgi-bin...?&I=LXFTY4&P=7