Originally Posted by McBTC

Don't know how many this may apply to now or in the future but if you notice a problem shifting gears on the cluster where certain gears develop a tendency to want to hop to the next larger cog, the issue may be a bent derailleur hanger and if so it's simple $25 fix. The bike shop has a special tool for that. I've got an aluminum road bike and the derailleur hanger is integrated into the rear dropout. It looks very beefy compared to the wall thickness of aluminum tubing but apparently it's made to bend so as not to damage the frame in the event it's exposed to some force or another. In any event, no amount of adjusting would've returned things to the normal operation I had become accustomed but a local bike shop took care of it (very simply too given such a reasonable cost).