I have a 2001 extended cab short box. When the tank is full the gauge will show full, then it will go to empty and the low fuel light will come on. After about 10 seconds it will go back to full. It will do this off and on until the tank is close to 1/2. then all is well. Does this sound like the sending unit? If so what is the best way to get to it. drop the tank or lift the box? I noticed in another thread someone said to put a good dose of sea foam? I usually don't have much luck with anything like that working, seems like new parts is what it takes. Thanks for any advise that I can get.