I have not had that problem with my TX (one month old). However, my TE developed a calibration 'skew' after about a hear or so. To calibrate it to b e usable at all I had to tap one target point high then the next point low and left. It never changed with time though.
there are some utlities for taking care of digitizer drift but I believe that they are designed for some of the older Plams that used the capacitive digitizer. The TX (and TE) use a resistive membrane digitizer technology which is entirely different and I don't believe it is possible to have software that can measure and correct drift. It should be possible to write software which could compensate for and skewing that develops. That is simply a case of mapping each pixel's position with regard to the resistance between resistive membranes at various points. However, I don't know of any software designed to do that with the resistive type digitizer. It would require at a minimum, a "target" point in each corner of the digitizer as opposed to only 2 corners and the center.
