So frustrated with this sending unit

[FLcustom10]

I have 8 gallons of gas in the tank. That really should be enough for the gauge to register. It works perfectly when I take the sending unit out of the tank and lift the float with my hand. As soon as I put it back in the tank it goes to empty and stays there. It is the same result whether I have the unit grounded to the tank or if I use a separate grounding wire. I have proved to myself that the float will in fact float in a bucket of water. I'm about to decide that it just won't float in gas. Could it be hitting the side of the tank somehow and binding? I can tie a wire around the float and lift it and the gauge will register, but when I release it the gauge goes back to empty. Shining a flashlight down there it looks like the gas level is at least up to the first indentation in the tank.