OK, the normal cause for this is the vent control valve on the charcoal canister. Sometimes it will seize up in the closed position and there is no place for the fuel vapors to go while you fill the tank. This results in the gas coming back up the fill tube and turning the pump off.
The canister is located behind the driver side rear wheel. The vent valve is bolted to it and has an electrical connector. Here is a diagram to help.
You can test the vent valve by removing it and then take 2 wires, run one off the positive side of the battery to the valve, then neg to the other. The valve should click and you should see the plunger move.
Sometimes you can tell just by looking at the plunger inside that it is shot.If it is all rusty there is a pretty good chance it is no good. If they stick open life is good and you don't have this problem.If they stick closed then this is usually what happens.