Leaking Fuel after getting gas?

[Myke783]

After getting my oil and rear differential fluid changed,
the other day. I stopped to grab gas (half a tank). I noticed my gas cap had a lot of pressure when I twisted it back on, even after trying to reseat it.
I drove home, took 5 mins, went inside. Came back out 30 mins later to see a huge puddle of gas coming out from under my gas tank. It was just steadily dripping.
It finally stopped, I jacked the car up, to try to trace it, it was coming from the top of the tank, like fuel pump area. I cleaned everything up, reset my gas cap, which didn't have the pressure anymore..
Drove it the next day, with no leaking at all.
Decided to get gas again today.
Well the same thing happened. I didn't feel pressure with the gas cap. But after getting home, it started leaking 15mins or so after it was off. Not right away.

Do you guys have any ideas, or advice on this situation?

[69 SS 350 5 Speed]

Your tank is leaking at the base of the filler neck or at the fuel pump gasket. Not a good thing. It needs to be repaired before some moron walks past your car and drops a lit cigarette.

[Rock-It Man]

Sounds like you overfilled.