Bunch of things could be causing the shifting issue. The hanger could be bent slightly. Does the shifter cable route under the bottombracket(see my comment above)? The chain and/or cassette could also be worn. Or the cables could just need lubing.
Where are you located? Any bike kitchens or co-ops that could work with you to help you figure it out yourself?
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C'dale BBU('05 and '09)/Super Six/Hooligan8and 3,Kona Dew Deluxe,Novara Buzz/Safari,Surly Big Dummy,Marin Pt Reyes,Giant Defy 1,Schwinn DBX SuperSport,Dahon Speed Pro TT,Brompton S6L/S2E-X
