[VetteVet]

5:30 is a little far for the gauge to swing to the right. That indicates that the resistor on the back of the gauge might be incorrect. Try running a ground wire to the terminal on the fuse panel and see if the fuel gauge swings all the way back to empty. If it does then pull the wire off at the sending unit and check for the 5:30 position on the gauge again. If it does the same then ground the wire to the sending unit on a good ground and check again for empty. If it goes to empty then the problem is in the tank ground or sending unit.
If you can, pull the sending unit and ground the flange and with the tan wire connected, move the float arm through it's travel and see if the gauge follows the travel. If it does you may have a bad ground on the tank or the float arm may be restricted in it's movement. A possibility is that the float may have a pinhole in it and it will only lift to the half tank mark because it has fuel in it.