Well, I finally went and pulled that big pig gas tank out of my Blazer and found the problem with my fuel level reading: The sender was broken off of the mounting plate that screws to the top of the gas tank and that broke the strap between the variable resistor and the bolt that screws to the sender wire. I had to fish the majority of the sender out of the tank through the hole to which it mounts. I then had to weld the broken off arm back to the mounting plate. I fabricated a new connection between the sender resistor and the bolt in the mounting plate and bolted it back in. Now I have a working gas gauge!