This thread was resurrected at an opportune time. Recently, I discovered my chain was worn enough to replace, so I was conscientious and replaced the chain, cassette, and worn jockey pulleys all at once. To make a long story short, the brand new cassette had gears that were out-of-true and I couldn't adjust the indexing to save my life. Luckily the old cassette worked fine when I dropped it back in.