I'll bet you a nickel it's the fuel pump.
Don't replace with aftermarket either, or you'll be doing it again! Spring the $200 or so for the motorcraft kit (the entire assembly including new screen, etc.). I haven't done this job yet, myself, but it doesn't look TOO horrible if you just take your time. The biggest trick will be getting the van up high enough for clearance and not snapping off the plastic filler neck guiding it down. I'd use 4 jack stands or, in my case, probably 2 jack stands and my oil change ramps.