2003 Jeep Liberty Fuel Gauge Stuck at Empty with P0462 and P0463 Codes

I have a 2003 Jeep Liberty where the fuel gauge is stuck on empty, even though the tank is full. The gas light is also on. I recently performed a partial fuel pump disassembly and tested the sending unit using a multimeter. When the float was pulled up, resistance read 270 ohms; when pushed down, it dropped smoothly to 20 ohms — indicating proper function. I checked the two center connectors on the feed harness and found 11.5 volts when the key was turned on with the harness disconnected from the pump. When connected and the key turned on, the fuel gauge slowly moved to full, then returned to empty when removed — suggesting a sending unit issue or wiring problem. I ran a diagnostic check through the dash circuit, and all gauges appeared to be functioning normally. Fuses are intact, and wiring appears clean. The sending unit is located at the bottom of the fuel tank and is part of a two-piece assembly with locking tabs that sit flush against the tank floor. I'm wondering if this unit is grounded directly to the tank bottom — could a poor ground connection be causing the gauge to behave incorrectly? The vehicle has been reported to have had a previous fuel pump replacement, and the fuel gauge never worked properly after that. It currently runs and drives fine, but the fuel gauge issue persists. I'm seeing OBD2 codes P0462 and P0463 — which are related to evaporative emissions system issues — though I don't see any direct link between them and the fuel gauge malfunction. Is this a tank ground fault? Or could it be a wiring or sending unit issue despite the resistance test showing normal behavior? Any insight would be greatly appreciated. Thanks!