Sounds like could be fuel filter. it is located near the front tank beside the frame. Need Ford specific tool to release spring retainer on the connection. Before changing filter you can do a fuel pressure test by attaching a check gauge. there is a schrader valve that a test guage can be attached to, on the 4.9 I6 it is located behind the right side of valve cover. Auto zone has loaner test thingys and tools.