You could try replacing the touchscreen controller. I have had instances on Bally Alpha 2 pro's where the touchscreen behavior is erratic, and replacing the controller would fix it. Does the screen calibration work any differently if the door is open all the way when you try to calibrate? In alpha 2's, when the monitors were in the open position the touchscreen worked, as I closed the door it didn't. I've never had something like that happen on IGT platforms, all the times I've seen the behavior you describe, it has always been the touchscreen glass.