Gas Gauge stumped !! Please help
 

Really don't know what to do next, I have a 1987 f-150, 351W carburated, dual tanks, Gauge reads half a tank, I have replaced sending units, tank selector valve, rocker switch in dash. When I switch tanks it still reads half a tank, pour some gas in both tanks still reads half a tank . Can someone please tell me what I need to do next. THANKS

any idea's ?? Please

Mine is same way, but never moves off of full, in fact, goes further past full when I turn the key on