I have a 98 k3500 with an oscillating fuel gauge. For example when the indicator shows 3/4 of a tank the needle will oscillate from about 5/8 of a tank to 7/8 of a tank. I am guessing at the rate of oscillation but would say it oscillates at about 15hz. I have owned the vehicle for about 3 weeks and it was doing it when I bought it, so I am not sure when it started doing it. So is it something in the instrument cluster or in the fuel tank? All of the other gauges work well.
Thanks