My new postal Metris van has developed this problem, slow fueling, after around 12 fuel ups, 2500 miles of dusty Kansas roads (rural route). I can see the fuel backing up in the fuel tube after the fuel nozzle kicks off at only few gallons filled...and then it will fill with 10 more gallons, with me slowly adding more gas. I am wondering if dust built up on a vent. No other issue.
edit, next fill up went well for 5 gallons, then slow. Wondering if just running it with less gas will help, maybe the filling to full tank is an issue, will experiment in coming weeks.