Since I haven't seen it mentioned yet: I have a 2001 F350 which I think is a clone of the OPs (I don't keep track of model year changes). I also have issues with my headlights being dim.
The first time I drove the truck loaded with the camper after dark I was convinced the headlights weren't even turning ON. The roads were extra black with rain and in the middle of nowhere with no street lighting it was pretty unsettling. I pulled over and walked around front to confirm they were working.
I assumed my headlights needed to be re-aimed so started googling for that when we made camp. I found a LOT of complaints from Ford truck peeps driving that vintage - and the standard stuff is thrown around as was here: clear/ clean lenses, different brands and types of bulbs, etc.
Somewhere I saw one quiet post about how the design of the wiring system is such that there's a big voltage drop at the headlights - for reasons unclear, the wiring doesn't supply a full 12V to them - it's a flaw (of wire size/ length). That being the case, the lights are just dim.
The truck is my DD in winter, and I've noticed the headlight aim is better/ different with no load in the bed, but they are still crap.
