I think I got an electrical issue with my gas gauge and this one is really confusing. I had my fuel pump replaced in September 2010 and I got 2 issues with my gas gauge now that were not there until recently:

1. When I have below 1/3 a tank, the gauge hangs near empty sometimes and even when I have over a 1/4 of a tank, the low fuel light is on. Fuel Used and the gas pump says I only used 10-11 gallons. When I have over 1/2 a tank it is accurate.

2. Tonight when I parked the truck on an uphill incline to check the mail, the gauge literally snapped to EMPTY and the LOW FUEL light went on. I got out and the gauge snapped back to full (the tank really was full). When I got back in it was on E again, but when I got in and slammed the door, it snapped back to F. It didn't do it any other time tonight on level ground. My guess is a loose wire somewhere, but since the cluster works fine but also seems to be getting bad data, I assume that the problem is under the truck. I am going to make an appointment for Friday to have the wiring at the pump checked for chipmunk damage (I always seem to find more nuts. They kept a nice store of them on top of the transmission and under the hood and even inside the frame rail), but what else should I check?

 

Yup mine has done that since Day One 3 years ago. If I put it in neutral at a light or while driving & the gauge is around 1/4 tank or less it'll bounce up & around.
I read on here that our gauges read in a variable reading while in drive. Meaning it reads averages between low & high & that's where it shows the needle when in drive or reverse. In park or neutral however it reads the actual/immediate level.
But like I said mine has done that all along & when I stop & am sure the gas isn't sloshing around any more I put it in neutral & watch the needle settle at what I believe is the accurate level.

But yeah you could have a connection issue & just because it "looks" OK when it's tightened doesn't mean it is. You should take the connections apart, emery cloth & dielectric grease when you put them back together.
All the bouncing around & door slamming does lead one to believe a connection issue. I'd start under the dash then look at the tank. On mine that's easy with the 3" BL & no bumper brackets though. Also there was a thread about a ground near the tank on the frame that can cause a TON of intermittent issues.

 

The fuel sending unit on the pump assembly is well on it's way out. Not much you can do about other than pull the assembly and try to clean the contacts.

 

Yeah our vehicles HATE anything but AC Delco/Delphi for electric/electronics. Maybe when it got replaced they used an off the shelf/after market brand?
But the door slamming to sometimes correct it does make me think of a connection issue. With the pump being replaced 2 years ago maybe things weren't tightened properly or came loose?!

 

It actually stopped doing it, but that doesn't mean I don't want to keep looking around.

I use Techron every month or so, so the contacts should be clean.

The different readings between when it is in gear or not explains alot. Sometimes the gauge behaves like that.

I will have the connections checked since I don't have a garage to use. Maybe stuff did come loose.

The pump is Walbro and has almost 22k on it. I bought it myself for $138 and it seems to work great.