Koyote

Thanks, that was my next question. When I pull off a worn cassette after way more than 3,000 miles, the lockring still looks like new. Why is this one all beat up?

mschwett : Hopefully you bought the bike from a shop...Because if it is only 3,000 miles old, you should take it in for a free tuneup -- and tell them that it runs poorly on the 11t cog. No way should that be happening after so few miles, and it does appear (correct me if I'm wrong) that, as SoSmellyAir suggests, the chain is dropping off the cassette.