Gas Tank Waterfall!

I have a 1999 Chevy Tahoe. The first time I went to fill the tank after I bought it, I wasn't paying attention and put 23.5 gallons of gas into my 21 gallon tank! It was taking a while, and I was just starting to wonder how much gas the tank would hold...and then looked down at my feet...I was standing ain a HUGE puddle of gas...and the river was coming fom a virtual waterfall from the top of my gas tank...it was a disaster! It took quite a while to stop "waterfalling" too and was a mess for the gas station to clean up! I haven't filled it since...'cus I'm scared of a repeat.

My queston is...it there and overflow on the top of the tank? Does it close agaiin after it is used? If not...assuming it is still open...would that affect the fact that sometimes fuel systems need pressure (or vacuum) for the system to operate properly? Could this be why my Tahoe stallas after idling for a while? Whatya think?

Gas Tank

I'm not sure if there is an overflow on the tank, but it seems odd that only 3 more gallons would have made it overflow. I also have 21 gallon tank but it consistantly take 23-24 gallons of gas. Maybe because I have an older model, a 97, but I was told by a gm technician that the gas tanks were the same until the 2000 and up model came around.

There is no overflow. It's probably a bad seal at the O-ring on the fuel pump/sending unit module, or on the fuel tank filler hose. You will need to drop the tank to fix it.