I agree the same here.....
My Excursion (which is the equivalent to an F-250) has I believe 5 leaves. I remember looking at this a few days ago after seen an older Dodge Dually and noted it only had 3 leaves I think.......
Something has been done to those springs..... which also means you cargo capacity and trailer capacity has been reduced...... I would say they are sagging because the leaves that are left are getting "tired" because of the increased load they are seeing..... I would say talk to Ford or a good Suspension Specialty Shop. Where I am from originally in Illinois, we have a place called Burke Spring Shop:
http://www.burkespring.com/ to give you an idea of what I am talking about. They do normal repairs now, but for decades they did Big Truck suspensions....... I have several friends that are farmers and/or truck drivers..... when anything below the frame rails needs repaired, it gets taken to Burke Spring...... PERIOD...... they will go there before they would take it to the dealer......
I would be very "easy" on the truck until I found out what you have going on....... One thing to keep in mind..... when it is "fixed" it will more than likely ride rougher than it does now....... just something to keep in mind.... I know my Excursion rides pretty good..... but it is definitely a truck, that has a full body with seats, not an "SUV" like an Expedition that is just a big station wagon..........
