It's a tough question is likely why no responses.
Have you replaced your fuel pump latley?
I know it's common when replacing the fuel pump on the 5.7's for the fuel gauge to become erratic. That is what happened to me. On the install instructions for the fuel pump the manufacture recommended replacing the electrical connectors at the fuel pump. When I replaced my fuel pump I did not replace the plugs and had an erratic fuel gauge right away. Since your truck is ten years ole it could be a sign that you are about to lose your fuel pump.
If you can get to the pump connectors you might try disconnecting those plugs and cleaning the connectors.
It could be a loose ground at the cluster.
I know checking for grounds inside the cluster would be a pain.