fuel gauge needle sticking

I believe my fuel needle is sticking. First noticed it when I filled up for long trips; the needle would stay at the full mark for a long time. Now when tank level gets to about 1/2 tank, it only goes up to 1/4 tank and then slight tapping will get the needle to come up a little bit. Is there any known problems like this or a way to test for this type of failure? I know on many Power Wagons, including mine, the fuel level sending system is prone to problems and by grounding the sensor wire the needle goes (should go) to full scale. Is there something similiar I can do to test the gauge on my Tahoe? The cluster is a Cadillac ESV Platnium. Thank you.

sounds like the sending unit is FUBAR.