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When filling the tank, the air in the tank has to go somewhere- which is to the charcoal canister. If the intake filter on the canister is clogged (if you drive a lot in mud or on really dusty gravel roads) or if the charcoal canister has been flooded and is now solid instead of porous, the the air will push back up the filler neck, against the flow of fuel, and shut off the pump.
So inspect the charcoal canister under the spare tire, or disconnect the line and blow it out with shop air.