I have a hunch its the fuel sending unit but dont know much else. Any thoughts? It doesnt move at all.

 

Its possible its a connector issue as well? I believe the body harness connector under the driver seat (on the bottom of the truck) is known to short and cause issues, clean that and apply di-electric grease.

If you know the pinout to the sending unit wiring, you could jump the signal to the return to see if the cluster reacts to this or not. If it does, then its likely the sending unit. If it doesn't, then its a good chance its the cluster or the wiring somewhere in the truck

 

Float might be dissolved or disintegrated. Happened to me. I fixed it by soldering a Holley 4bbl float to it worked great.