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.