Ok, first ive just replaced my cassette with XTR and my chain with a Scram PC99. I took it into a shop to get the shifting adjusted. It shifts wonderfully now. Although when I pedal really hard up hill the cassette breaks loose, it feels like it slips for a pedal stroke then engages like normal. I don't think the chain is jumping to another gear because it stays in the same gear and everything shifts fine. Do I need to torque my cassette down harder? I only tightened it to where it felt good... but im second guessing whether i should have used a torque wrench. Or, is it something in the wheel like the sealed bearings going bad? It didnt do this before I replaced all this stuff.