I'm afraid this is not a hardware problem, a lot of people on
this thread share the same problem. The Ziphone messing up calibration tables rumor has popped up quite frequently here and there on this and other forums, but I'm not sure this is the cause. On Ziphone unlocked 1.1.3 and 1.1.4 I didn't have a problem, it was only after I upgraded to 2.0 that the slider issue started, and downgrading back to 1.1.4 only made it worse.