If you follow through with the recommendations posted above regarding cable housing, new cable, checking cam position on the shiftmate, and still don't obtain better shifting consider replacing the g spring in the shifter. Also consider checking der. hanger alignment.

I had no luck getting SRAM rear derailleur to work with Campy shifters whether I used SRAM or Shimano cassettes or the appropriate Shiftmate. Current setup is XTR 9 speed derailleur, Shiftmate, Record 10 speed brifters and XT 12-34 cassette.