I've had this problem since I got my 2012 Cinder Cone:
Shifting the rear gears is no problem, up and down. Only until I reach the two biggest sprockets... Then the chain and derailleur start playing funny.
Clicking the shifter from the smaller sprockets up there is "one click - one shift" smooth work. Then when I get to the second biggest one I can hear and feel the chain wants to go up even more. Like the cable was too tensioned. When I shift right to the top and then one down the problem is noticeably even more - the chain jumps between the two sprockets, trying to stay on the biggest one.
When I loose the cable tension it's a bit better, but then to shift up from any position I need to do a "click and a half" thing. Very annoying, especially when reaching these more technical climbs...
The mech is Shimano SLX, shifter Alivio 9-speed, cassette HG-53. The chain has been replaced regulary (it's the 3rd one now), the cable is fresh too (Shimano XTR). Where is something wrong?
Is it the shifter's fault?
Marin Indian Fire Trail '93. Build to be ridden, not to be watched. Stolen - not forgotten! Awesome bike...
Kona Cinder Cone 2012 - it will be retro in few years time.