Chain skipping mid cassette after a clean I have cleaned my chain and gears with rubbing alcohol and towels. Afterwards, I applied some chain lube on the chain. Now, when under a lot of torque, the chain skips and slips mid-cassette. Low gears and high gears seem to be unaffected. There were no tweaks made to the front or rear derailleurs. Could the previous gunk have kept the chain centered on the gear? Is there any chance that the rear derailleur got tweaked in the cleaning process somehow? I did clean the two gears on it.

The bike is a 2007 Specialized Tarmac with about 4-5,000 miles on it.
It's possible that during cleaning a grain of sand, for example, has become stuck in the chain causing a stiff link which does not travel cleanly over the cogs. Cleaning chains and cogs often involves a significant amount of moving dirt around before extracting it.

A simple test for this is to move the chain through both hands bending every link. You'll find a stiff link very easily.

If that's the problem, clean the link until the stiffness goes, re-lube and you should have no further problems.