When you said that you checked all wires and grounds, please explain how you did this.
From the fuel gauge there is a yellow wire that runs to the fuel tank sending unit. With the key, on what did the gauge read when the wire at the sending unit was disconnected? What did the gauge read when the wire at the sending unit was grounded momentarily? (Note: do not ground the wire at the sending unit for more than 10 seconds or damage to the gauge could result)
The fuel and temperature gauges can be calibrated, but if your gauge is always reading full, calibrating the gauge will not correct your problem.
Here is an article that Gil Baumgartner wrote on checking the operation of the fuel and temperature gauges.