FUEL Gauge

Sounds like a cracked or partial sunk float to me. Generally the tank gets a pretty good ground simply from being bolted into place and the grounding clip from sender spigot to fuel line does squat. Take an ohm meter and put the leads from the car body to the face of the sender unit. Should read zero, after you see that it's not a ground issue. Take the sender wire off the sending unit and short it to ground BRIEFLY, fuel gauge should go full scale.