fuel gage, calibration?

That gauge never was gallon to gallon accurate. It should show full when the tank is filled and show empty before you run out of gas. The earlier gauges were more sensative to small signal changes when new. Those generated a lot more heat internally so those didn't maintain their accuracy or live as long.
Chryslers engineers sacrificed some of the accuracy to lower the heat and extend the life of the gauge. They realized it is just a range indicator. The change helped lower the number of Chrysler products sitting on the sides of roads out of gas.
A little technical info, Earlier gauges contain 13.3 inches of ni-chrome winding with resistance value of 1.5 ohms per inch at 70 degrees. 20 ohms total resistance
Later gauges ( yours) contains 12.5 inches of winding with a resistance value of 1 ohm per inch at 70 degrees.
The only change in the sender was in its shape. Its float nolonger bouces on the bottom of the tank.