If you plug in your TS to a windows box using touchkit drivers, is it the same deal?
If so then I would say busted overlay. Are there any cracks or deep scratches or anything on the overlay? Anything in the casing pressing against the screen somewhere? Do you have your screen mounted somewhere where it could be twisting, like a custom housing that was too small but managed to squeeze it in there somehow?
My bet is that a new overlay will fix your problems. $50 from either the store here, digitalww, or eBay.