My fuel gauge jumps all over the place, whenever it feels like it. I was told it was my sending unit, and since it's part of the fuel pump, and the fuel pump is in the tank, I have learned to live with it. I'm guessing you may have the same issue, or an issue with the gauge itself.
2001 GMC Sierra 1500HD/Sunset Orange Metallic
You can set my truck on fire, and roll it down a hill, and I still wouldn't trade it for a Coupe DeVille.