If you are fortunate, it will only be a ground. I've had two of these recently, and both were the sending unit, however (including my wife's Astro). If you determine that's the problem, you'll get to drop the fuel tank to repair it:
Pull the tank unit:
Remove the level sensor:
...And repair the sensor. The bifurcated wiper contacts on the resistor assembly lose their tension, and the pivot works loose. The two factors combined is enough to cause an intermittent loss of contact and drop the gauge to ZERO.
While the tank unit is out, it would be a good idea to check the pump and sensor connectors in the op of the tank. They tend to overheat, and can be replaced with an upgraded aftermarket harness assembly.
