Gas guage stuck on full

We have a 1984 chevy van and the gas guage is stuck on full.  We are also unable to put more than $3.00 worth of gas in the tank without it overflowing.  Any help would be appreciated.

If its overflowing, its full.

No, our gas tank is not full.  We can only put in $3.00 let it drain down in and add more and let it drain again.  It takes about 15 minutes to put in 10 gallons.

there is supposed to be some kind of vent to allow you to put gas in and let air escape as you do it- look for info on that, it sounds like yours is plugged