Refueling Problem

[lyricsdaddy]

Hello all. I have recently bought, say 3 months ago, a 78 GMC C25 pickup. Its got a 5.7 and one gas tank. Since I have bought it, I have been having a refueling problem. I have to pump really slowly, or else the gas overflows and pours out onto the ground. Also, once the tank is "full", it does the same thing. But the gauge never reads full, even pumping really slowly, and it starts to pour out, the gauge only reads between 1/2 and 3/4 full. I have no idea whats wrong, and could use some help. I havent been able to find anything usefull anywhere else, unfortunately. Thanks for all your help! If you need to know anything else about the truck, let me know.