2001 Silverado 3500, Duramax Diesel LB7, dual fuel tanks. Problem happened suddenly. The fuel gauge always reads empty and low fuel alert is showing. The sending units (dual tanks) are new. Both are AC Delco. When I ohm test the wires from the sending units at the PCM, both correctly read around 40 ohms when empty and around 200 ohms when full. Or, almost full, I only had so much fuel on me. When I use a scan tool to monitor fuel level, it correctly reads the level (%). I siphoned fuel out and the reading went down. I refilled the fuel and level % went up. When I unplug the cluster and reconnect it with the key on, the fuel gauge does an instant sweep to full and sweeps back to empty. So, I think the stepper motor is ok. The needle hadn't been acting up before this problem suddenly happened. Is there something in between the PCM and the cluster that can go wrong?