I just found and fixed my problem I had with my fuel gauge not working. Turned out to be my float. The float had gotten some gas inside of it and was weighing it down making my gas gauge read empty. It was weird because it DOES float in water but will not in gas. I figured that out with my fishin line, lol. Anyways, I called up my local Ford Dealer and they had them in stock and were only $7 for one of them. Totally fixed my problem. Maybe your issue might be the same.
Take your fuel pump/sending unit out and pull the float (looks like a mini alluminum keg) off of the arm and shake it around. If it has liquid in it, replace it cause thats your problem. If not, The problem lies in your sending unit if it isnt any fuses/harness'. Also might want to check your gauge (pull the plastic off your gauge cluster and very gently move your gas gauge. Then turn the key to the truck and if it moves back to empty, the gauge is good. Investigate Sending unit).
Let me know if you have any questions.