I have just purchased a used 2000 30' Winnebago Motorhome on a Ford F-450 chassis, and have filled it up about 6 times in the last 5 weeks and find it takes about 20-minutes to pump 45 gallons of gas. It has a 55-gallon tank, but will only fill on the very slowest speed... not even able to be placed on the "1st click" on the pump nozzle. I literally have to hold it straight up & down and barely squeeze the nozzle trigger or it back fills the filler tube and shuts off the pump. Do I have a blockage? Is this unusual? Please, if any of you have had the problem, please respond with a fix. Thanx.