2002 Ford Explorer

Our car has been lurching forward as if it is going to cut off (while driving). We have had it checked and it’s not spark plugs, or any thing like that. The mechanic told us he thought it was from us “topping off” the gas tank when filling it up. Neither my husband nor I have done this. Normally the pump shuts off when the tank is full. I haven’t topped off a tank since the early 80’s probably. The mechanic said that there was gas in some line or area that there should not be any b/c the tank was too full. I had told my husband that my common sense was telling me that whatever sensor or device that shuts off the tank when the gas vapor level gets high enough, was probably broken, but we got the line cleaned out anyway. The car seemed to be ok until the next time it was filled up (at a different gas station). It started lurching again after that. What would your guess be as to what might be the problem? I would like to have it fixed but have some idea of what is wrong so that I can better explain the circumstances. Thanks!