My gas gauge just started to move from full to about half a tank, then back up to full, then back down and back up etc. It does this slowly, truck has about 170,000 and this has never been an issue until today. Did a lot of gravel roads today and hit some one hole that shook things up, but that is not unusual.

Any ideas what I should check first? All other gauges work fine.

 

The sending unit is part of the fuel pump, which is located inside the fuel tank. I suggest you live with it for now, at least until you have to replace the pump.

 

That is what I suspected and was hoping there was something else that was easy to get to. Dropping that tank to get to the fuel pump and sending unit doesn't look easy. Thanks for your reply, maybe it will magically just start working.

 

try a steady dose of techron fuel treatment for 2 or 3 tanks. it has a 50/50 chance of cleaning the sending unit.
http://shop.advanceautoparts.com/web...ontent=7081073

 

Check the electrical connections at the tank as well. Might just be a bit loose.