My just-over-1-year-old Palm TX (ie, just out of warranty) began the giving me the pain of digitizer drift. That's where you need to pick below buttons and other points for them to activate. Using the Preferences | Touchscreen calibration tool just makes things worse, because using it seems to force the misaligned digitizer to get worse.
I did some reading on the Internet, and found it is a fairly common problem, although not one that has affected me for ten years and through five PalmOS devices -- until now.
I tried a few different ways of touching the Touchscreen calibration tool, and finally found one that works.
Instead of picking the center of the three bull's-eye targets, I found that it works better to drawn a circle around each target. In each target, I moved the stylus in a circle around the smallest red circle. The PalmTX was happy, told me I passed the test, and the touchscreen is now correctly aligned.
On second thought, it appears it was not the circle movement that worked, but touching the targets too high. Touch the target points higher than their centers. You may have to try a few times to see just exactly how high to touch.