Just a thought!
I had a 02 Ford 1 ton Van while working for Snap On, going to work one morning I heard a pop and a cycleing hissing, turned around went home and found a spark plug had blown out, broke coil over. I talked to several of the Ford dealers around and they said they fix 2-5 of these a week on the 5.4 motors from I beleive 1999-06, there was an engeniring mistake that only left 3 coils for the spark plug to engage and be tite. The only fix was REMOVE the cylinder head from motor tap , helic coil and replace head, $2500 dollors with NO Warrantee because they said it was a 50/50 chance of that one going again or another one., moral, even a heavy duty truck can have problems, only hope there fixed befor you hit 100K .