spacers are fine
tension...I've thought about it tons....I completely re-adjusted the RD yesterday as well. In setting the L limit screw, I loosened the barrell adjuster so it was just a little slack, then set the L screw by tightening the cable with my hand rather than the shifter (per the excellent instructions from the Park web-site). It was doing the same thing then...I hoped the problem would go away when I re-tightened the cable and started using the shifters...no luck.