Put a new chain on my Tricross Comp last weekend. The casette didn't seem worn - I think it's got about 4k miles on it - so I didn't replace it.
Now, when I really have to mash - like standing up a hill, or when I'm starting out and left it in too high a gear, the chain seem to slip/skip. Now, it could be a shifting/derailler issue - I need to replace the cables this weekend. But is that a sign that perhaps the casette is in fact worn and needs to be replaced? How many miles should a casette normally last?