Is it the chain or the cassette?

[Alex Ramon]

Usually if it's the cassette, the chain will skip forward a tooth, but if it's riding on the teeth it sounds like it may not be shifting properly. This could be a gummed up shift cable, or more likely a bent derailleur hanger. Since you've changed to a new frame I'm guessing the derailleur hanger on the new frame is slightly bent. If that's it sometimes you can straighten it by hand, but it's better to use an alignment tool like this one. It's pricey though so it would be cheaper for your local shop to check the alignment to be sure.