I have an erratic fuel gauge. I have to reset odometer at every gas fill up to keep track of mileage. Quoted $600 to replace the unit but I tried the GM Fuel treatment Plus in the gas tank first. Anyone have luck with the treatment resolving the problem?

That must be some pretty special treatment to repair a fuel sending unit!

The fuel level sensor is a variable resistor with a floater on an arm. The part cost $120 from rockauto, or you can replace the whole fuel pump assembly which is a $200-$300 part depending on brand. The fuel tank needs to be taken down but apart from that it shouldn't be very complicated job.

I've also heard there is an electrical connector in the floor behind the driver seat which if it corrode will amoung other things cause the fuel gauge to behave erratic so you should probably check that first (not sure about the location though)

Sverker is correct about the harness connectors in the floor, driver's side, approx behind driver's seat....just take apart and look for "green" corrosion....if ok, then disconnect harness going into tank.....turn key on....should read full...get a 140 ohm resistor.....attach it to the harness connector for the fuel level circuit....if it reads half full, you need a sender....