Here is another thing you can try. The sending unit is variable resistor. It’s 88 ohms for full. 44 ohms for midpoint. And 1 ohm for empty. You can buy these resistors online cheap. If you can identify the wire from the sending unit to gauge, you can disconnect from the sending unit and hook up the resistor from the wire leading to the gauge and then to ground with key on to determine the accuracy of the gauge.