Originally Posted by HWS
I have recently found on my Fuji, that if the rear skewer isn't tensioned properly, the chain keeps trying to jump to a different cog while riding. There is a noticeable deflection of the RD when tightening down the skewer, and this causes the skipping problem.
Should there really be that much deflection in the frame from tightening the skewer that it would cause the RD not to line up properly?
I'm guessing that your dropouts aren't parallel. Better than average bike shops will have a tool for checking and aligning dropouts.