Could be a ground issue, check wiring for loose, broken or corroded wires.
Sulfer from the fuel could be built up on the resostat of the fuel level sensor in the tank. Try using a good quality fuel injector cleaner in the tank and see if it affects the operation. If it is a build up of contaminates on the sensor, this may clean the contacts. I always suggest this with fuel gage problems like you describe, I am in NW PA and our fuel has a high sulfer content, I see it quite often.
With the age and mileage it could be an issue with the gage in the cluster, I've only run into that being the cause of your condition once though, and the needle was stuck just above 1/2 a tank and would not move.
Here's a couple of ideas, let me know if they help.
Dan
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Wednesday, May 5th, 2021 AT 12:07 PM