by what you describe i'd be fairly certain it is your clutch slipping

as for the sprocket nut i wouldn't worry, they usually put a ton of super duty loc-tite on those things, and then all that heat coming right off the motor just bakes it all together... it was very very hard to get off of my gixxer and at that time it was only 6 months old, so i can only imagine how much almost 6 years would fuse it on there

but if you want you could take out your clutch plates and measure them with a caliper, get a service manual and see what they are supposed to be, but you might as well just replace it if you've got it out, looked up a Factory carbon fiber clutch set and its only 61$ retail