Before I put the sender in, I tried it with the gauge. There was a huge dead spot. The float arm was 3/4 up when the gauge finally read anything, but at least it did go all the way to full. My factory gauge never did that. Right now I have about 14-17 gallons in it, and the needle barely comes off of E. Clearly, it's not the gauge, as it now appears to be the sending unit.

For now I guess I'll just burn through this tank of gas. No sense in draining out a full tank. Once empty again, I'll try working on the sending unit itself.

Dobie, mine did the exact same thing(huge dead spot). The reason there is a dead spot is that the copper tab I pictured above is not making enough contact with the varying resistor. The solution is to bend the copper tab up so that it makes a harder contact.

I'll definitely try that. Any reason though why it worked better out of the car vs. installed in the tank?