This comes up often. It is answered frequently.
Ford built the returnless fuel pump system with an inadequate filter screen on the bottom of the fuel pump module. The filter screen is either too small or too fine or both. Eventually the screen plugs up on all of them and when it does it will cause a problem just like you described. Usually you just need to take the screen out and throw it away. It isn't needed. There is still a conventional sock filter further inside the pump module.
To see what you are getting into go here:
http://www.contour.org/mods/mods.php?s=howto&displayid=39Look at the very last photo to see the screen in question.
Most likely that is all you really need to do.
