I don't know exactly what your truck is doing but if you can only use about 3/4 of your tank then the strainer on the bottom of the fuel sending unit could be broke off. I don't know where exactly to get one but I had that same problem with my truck. If you are just having delivery problems then cleaning it or replacing the fuel filter in the engine compartment of your truck may help.
Yes the ford Excursion diesel has one big and two small fuel screens inside the fuel tank, the two small ones are inside the plastic housing, to clean them you must drop the tank,remove the sending unit,carfully dissasemble the plastic housing on the steel intake tube and remove both screens, they are about 3 inches long and 1/2 inch wide. these can plug up and cause a miss/ no-power problem with NO check engine light coming on, this is the first thing to check before spending all your money on parts!