Dealing with a 1999 GMC Safari SLE w/ 4.3 v-6 motor. What I am dealing with is a fluttering fuel gauge. Replaced the fuel pump and sending unit w/sensors as advised by a reputable garage, still have the fluttering gauge.
There is a service bulletin out I listed it below. It has limited information on it. I would call your GM dealer or GM themselves and give them your VIN number and see what it is about.
Engine: FUEL SYSTEM, OTHER: STORAGE: FUEL GAUGE SYSTEM
Service Bulletin Number: 3046A
NHTSA Number: 10009382
Model Years Affected: 1999, 2000, 2001, 2002, 2003
Date of Bulletin: 09/2004
Bulletin Summary: FUEL GAUGE FLUCTUATION IN PARK OR NEUTRAL.
You can also check the grounds to the fuel tank, if they are corroded or making bad connections it can duplicate this problem. The fuel gauge may also have the same problem. Check on the service bulletin first and go from there.
Let us know how you make out.
The dealership service department should have a very helpful tool which sends a signal (just like the fuel tank sender) to the instrument cluster (gas gauge). This could be a great help in diagnosing the problem.
It could be a bad ground, poor connection, or the cluster itself.