The motor is talking to you about it not liking something at that RPM, understanding what is saying Is the hard part AKA aside, I would try reversing what you did with the mechanical advance and have it all in by 2000 instead of 3400 RPM.
If that doesn't fix it try replacing # 7 spark plug with the next hotter range plug and see if that helps it or not Maybe you have a intake gasket sealing problem on # 7 Is that plug shiny or dull looking?