This one has been discussed before on 660s. Seems odd that idle would have something to do with shifting, but it does. Turn your idle screw in clockwise while the Rhino is running at idle, (make sure its warmed up), until it dies. Then, back it out 1/8 turn start it back up and adjust to the lowest idle that allows it to run. That should allow you to shift in reverse and low without feathering the throttle. This method worked for me.