bo,
I believe the manual says 7500, with motorcraft 5-30. Which is syn-blend. There is also a section for severe duty. That calls for more frequent fluids changes.
I would classify severe duty as constant towing or hauling. everyday use in severe climates especialy high temps. IMO that would be the middle east of sorts. Maybe even includes severe cold.
Despite my spirited driving. I dont include my trac as severe use. At least not like the performance street cars I built. I did oil changes on them 4k to 5k. Even in the day before synthetics or blends. Sometimes 3k or less, if they saw alot of trac time on dino.
IMO, if you are not beating on it. 3k to 5k changes on modern motors. Is a waste of $$ and resources.
Fluids cost to darn much. To not use them to their full life potential. Modern motors that fail nowdays. Is not oil change related. Unless you never service it. Or related to part failure, non oil related. Except a bad oil pump. Or using the wrong oil, for the engine build clearances. Or the motor wasnt assy properly, and bad parts got past QC.