gas gauge!!!!

the gas guage in my 88 c/k1500 V8 5.0L 1/2ton 2wd GMC pickup truck seems to be broken. one moment it says I have a full tank but the next it tells me that Im completely empty while I still have gas in my tank. it also, if i dont drive it for a few hours, it kind of resets but as soon as i turn it on, the gauge slower goes to full or empty and stays there. do any one know what might the problem be?

I Had a truck with that problem, and found a bad ground at the gas tank, and it can also be the sending Unit in the tank.

I found the ground wire near the tank but how do i figure out if the ground wire near the tank is bad?

pull on it! is it loose? i had a 94 and a 2000 that did this. i was told it was the sending unit itself. I could go 50 miles after the low fuel light came on. i never figured it out it didn't really bother me that much.