Yeah they are worn. The new chain is hopping like crazy under tension when I shift to the middle gears.

Now I have a decision to make.

1) replace the cassette, and return the cassette I purchased which doesn't fit my wheels.
2) replace the rear wheel which does have a slight hop that I was told is impossible to fix and use the cassette I already have.

EDIT: decided to just stick with my current wheels. I got a replacement cassette from amazon.