I filled up my tank Thursday night, and didn't go anywhere on Saturday. I thought it seemed odd I was down to a little over half a tank, then today on the 9 mile ride home from work, it went from one notch above half to one notch below. What the hell is going on?
I wonder if the sending unit in the fuel tank is bad. I know that GM had problems with 99-01 or 02 where too much sulfur in the gas would corode the sensor causing it to have inaccurate readings. Don't know if this is your problem or not.