I guess it sounds like I am one of the many that have had this problem too. It only seems to happen in the sand. Never in the mud or on a hard packed road. I thought if it was the chain skipping on the sprocket, the rear sprocket would be missing teeth, or the teeth would be rounded off. This does not seem to be happening. Also thought it was the sprocket carrier slipping on the axle, but marked it and it is not. Also if this was happening, the splines on the axle should be stripped by now. I have an aftermarket skid plate on it, and can only sumise that it is sand building up and going through the rear sprocket. I am hopefully going to take off the skid plate and try riding it this weekend and see how it goes.