The only other thing I can think to do is make sure you have 12V at the fuel sender plug. You don't say if you measured that or not. As a general rule; if you have 12V at the plug and ground the fuel sender wire, and get zero reading on the fuel gauge, the gauge is dead. Sorry about the bad news.
A bad ground strap across the rubber fuel line leading out of the sender will cause the problem you are describing, but by grounding the hot side the ground strap is effectively removed from the circuit and is not an issue. If you ground the hot lead and the fuel gauge works, then quits when you reconnect the hot lead to the sender, you may have a bad ground strap or sender.