Fuel guage problem

Hello I just bought a 95 camaro z28 and the fuel guage does not work it is stuck at the half a tank. I will drive it 120 miles then fill up. this last time the guage actually went to empty and when i filled up the guage pegged out past the full mark and the went back to the half mark and has been stuck there ever since. Any suggestions?

Shoebox has a procedure for checking fuel gauge problems:

http://shbox.com/1/4th_gen_tech2.html#fuel_gauge