I dug into the 05 service manuals.... hopefully your vehicle model year isn't too much different. Since you neglected to tell us that important piece of information I don't know.
In the 2005 GMT800 trucks...
The fuel gauge is a loop from the PCM through the sender rheostat. The PCM then provides Class II serial data to the instrument cluster... The fuel gauge doesn't rely on a frame ground.
The fuel pump does rely on a frame ground.
Nearby grounds are as follows...
The G401 ground is on top of the flat plate on top of the round crossmember behind the rear axle on my 2005. This may be the rear lamps or it may be the fuel system.
The G302 ground is on top of the over-tank crossmember mounting bolt above the LH frame rail on the HD & 2500,3500 models and on the 1500 it's on the forward cab mount off the frame.
The G110 ground is on the forward cab mount off the frame.
A sharp jerk on the Metripak connector at the fuel pump, from the fuel tank sharply dropping further than the slack in the harness, might've damaged the fuel sender/pump wires, terminals, or connector.
You aren't showing a P0442 or another evap code so the tank pressure sensor, which is a separate connector, is probably still making good contact in its' loop from the PCM.
My guess is you damaged the Metripack 150 connector to the fuel pump. The easiest way to deal with it on a GMT800 is to pull the bed and take a look. DO NOT USE AN IMPACT GUN ON THE BED BOLTS. You'll spin the nuts in the sheet metal housings with an impact.
