Fuel Gauge issues

[84GMCdiesel]

Ok, been trying to solve my fuel gauge issue. I have a 1984 GMC 1500 2wd long bed, dual tanks, 6.2L diesel. Both tanks when full will only read just under half on the dash gauge. I cleaned and reattached the sending unit grounds on the truck frame and checked the dash gauge itself. Still can find the issue. The gauge will move as I burn off fuel and when just under 1/4 full I can take on about a half tank. Its like the gauge is only using half of the normal range. Should I try a new gauge or did fate happen and both sending units go on the fritz? She only has 52K original miles on her, but she has the age for them to go bad. Everything else works except the AC so I would like to get this fixed, along with my missing stuff for the AC. Thanks for all the help. Mike