Recently acquired an old M300 and would like to upgrade some components. First, the chain slips when I really dig into it. Is this most likely a worn cassette? (could also be combination of cassette, chain, and front rings?) Second, can I replace the solid fork with a single (Headshock?) or double shock? Any other upgrades anyone can recommend for this bike? I'm not a racer or downhill rider, just cross-country trails. Where is a good place to research compatibility? Thanks for any help!