I'm having a problem with my gas tanks. At almost every gas station that i go to to fill up, every time they start to pump the gas the pump clicks off like it was full. Now usually the tanks are bone dry and it is doing it to both of them. I took the hoses out to see if they were cracked maybe the pump was picking up fumes and turning off because of the emissions laws in jersey, but all of the lines are fine. The truck is a 91 Ford F250. It's kind of a hard problem to describe but i can't seem to figure out why the pumps keep shutting off. If anyone has any theories on this they would be greatly appreciated. Thanks in advance.

-Joe