Gas gauge is not working correctly

Hi,

Most likely, the rheostat is bad on the float gauge in the tank. A rheostat is basically an electrical device that controls voltage by resistance. As the float raises in the tank, resistance is lessened allowing more power to make it to the fuel gauge. When the float is low, resistance is high and less power is sent. What happens is the rheostat is likely bad in the section.

I attached a pic of the pump assembly. I circled the rheostat and highlighted the float.

Let me know if you have questions.

Take care,
Joe

This in unfortunately a common issue in a few years of GM vehicles. The problem is that the sending unit in the tank develops a bad spot and you get erratic gauge operation. The repair is to replace the level sending unit. The catch to that is that in order to replace it you need to drop the gas tank, remove the pump and sending unit, then replace the sending unit. In this case I would probably replace the entire pump module with a new OEM unit because of the year and mileage on the truck. This will give you an idea of the process:

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

Being yours is a GM it is a bit different but not by much.
https://www.youtube.com/watch?v=u1EnB4V1Vi8
https://www.youtube.com/watch?v=3mjaQv-VcZU

The reason I say to replace the entire module is two fold. One your pump has a lot of miles on it and they are somewhat known to fail between the 150-200K mark, usually earlier in my experience. Second, the level sending unit alone is almost 30 dollars more than a complete new OEM pump assembly with a new level sender on it! There is one item to know though. The newer pump units come with a better updated connector to replace the one that likes to melt on the older pump assemblies. However they include the instructions and parts to make the change.