Just to reiterate what I did:

I tested thecurrent 'better" repop I have as well as the last one outside the tank....hooked up the wire and the ground and tested that way.....the gauge registered full when I raised the arm to full, and measured empty when at rest at the empty end of the swing.

It just seems like the unit itself is calibrated wrong for the tank.....the dead spots are a seperate issue, as once I tweaked the first couple units for the level it seemed ok aside from the dead spots.

In my case the original sender didnt work at all...I did compare it to the first (cheaper) repop and tyhey looked basically the same aside from the repop seeming "cheaper". I have since tossed the original (dumb move). The "better" repop appears to be the same as the cheaper one in terms of measurements.

I am convinced that the gauge itself and ground are fine.