My 2000 yukon gas guage varies from showing low fuel light be on to over a quarter of tank. This is not due to unlevel ground sitting still level it moves back an forth.Was wondering if anyone had this happen and is there anything besides in the tank that would cause this. DAVE

Sulfur contaminated sending unit possibly. Add some Techron to your gas. My '02 Corvette had a serious case and I heard it affected other GM's also.

Sorry guy but mine did the same thing, jump from full it empty and never seemed to mater when or what i was doing........sending unit in the tank is the cause.
good luck!