Fuel gauge gone goofy

[Rich69shortfleet]

So, is it gauge, sending unit or wiring?

Had the cluster out recently but everything worked fine after reinstall. When I filled the tank recently it looked fine. Then the gauge looked like this when I stared it up the next time. I've logged about 30 miles since and it moved a bit but is still way off scale. It has gone way off scale before after sitting but always corrected when started.

I'll check the connections at the cluster but not sure what else to check. And since the needle has moved it is connected to something. All parts original to the truck.