Gas drips underneith when tank is full?

2nd time now... I fill the gas tank and it starts dripping(at a good pace) from the underbelly. Is there a over flow line? I made sure I did not over fill it. Thanks! after I drive it about 40 miles it stops

1998 Tahoe 4dr 4x4

Either the seal on you fuel module or the fuel module itself is leaking.