My 1981 1/2 ton 2wd with a single driver side mounted tank has what i feel is a strange problem while fueling her up. When fueling at any gas station i have to hold the nozzel upside down in order to pump gas into the tank. If i try filling her up while holding the gas nozzel in the normal manner it kicks off the nozzel fuel flow ( just like when your tank is full) and I cannot pump fuel. Not the original owner and has done this since I bought it. I did check the filler tube assembly for a kink but it looks okay. Any Ideas guys ??