[VetteVet]

Your first sending unit may have had a pinhole in the float which would have made it heavier than a full tank of gas could have lifted it. The second gauge would have red the same with that sending unit. A bad ground or sending unit wire will cause the second tank sender to give the over full reading, as was said.

Run a temporary wire from the sending unit flange to a good ground and run a new wire from the sending unit terminal to the gauge.
Alternatively you can pull the sending unit and ground the flange with the terminal wire attached and move the float up and down with the key on and watch the gauge for movement E to F.

The 67 to 72 models run the sending unit wire to the fuse panel to the FUEL terminal and from there the wire goes to the fuel gauge in the dash. I am not sure how the 82 is setup.

If you ground the sending unit terminal on the fuel gauge it will read to empty.
This should tell you if the gauge is OK.

Since you got the same readings with 2 gauges on the first sender, I doubt that the resistor on the gauge is bad. That will usually cause the gauge to read up to 1/4th tank and no more.