Fuel Tank Gauge

I'm having a problem with my fuel gauge. Whenever I fill up my tank, the gauge only reads half full. The gauge goes all the way to empty after about 100 miles, and then I have no idea how much gas is in the tank. I know its not the sending unit, I bought a new one to test it, and it does the same thing as the one that's in there now. If anyone has any ideas why the gauge is doing this, I would appreciate any advice. Thanks alot!

-Matt
 
1. Pull the wire off the fuel tank sender & ground the wire. Turn the ignition key to acc/on, if the fuel gauge reads full the gauge is good.
2. If the gauge is good you will have to bend the float rod on the sender. This is very common with new senders.