It seems my gas gauge is always on full. It does not move. Any idea where to start . to repair....thanks

 

look here shbox is good. 4th Gen LT1 F-body Tech Articles

 

Get a 1/2 watt minimum resistor, 40-50 ohms, unplug connector at tank or body harness, put in one lead of resistor to tan wire of body harness to gauge, and other resistor lead to ground.
Turn on ignition to IGN and gauge should move to 1/2 tank, or so.