What tyre pressure do you run.. cant think anything else, spring on 5, and im sure youve seen the two settings on the spring.. Other than paying £40-£50 to set susp up just to see i dont know..
Do you have a fellow rider for a second opinion? Maybe swap bikes see if you feel the same about his? And him yours?
When you had the shock off .was the swingarm free to pivot? Does it "flow," ok when you compress it to set the sag. And no offense. But are you nutter on the road or is it normal road riding that's the issue?
How's the front set up? To soft on the front can make the back feel harsh. I like that someone suggested a suspension setup.. I plan on getting mine done this year.