Vibration at 80-100k in a 4x4 Ford 350 diesel superduty

2003 6.0 f350 Power steering pump - YouTube

There are a couple of things that can cause vibration ie wheel balancing that might be wrong usually vibrates when driving at 100-120 km/hr,ball joints that a worn,wheel hubs bend,steering knuckle excessive play,steering rack excessive play,worn steering UJ,worn steering column....

If the vibration is in the steering wheel, and you are in 2wd then chances are it is not you're u-joints. I would get other car on a Lift, check ball joints and steering linkage for play. You may jut need to balance your tires

With diesels all you really have to do is change the oil, fuel filters, air filter, and transmission filter. If you have 4x4 get the differentials service as well as the transfer case and you should be good to go.

cehck tie rod ends on steering. Or loose suspension part.

ball joints and tie rod ends are the most common cause of this in superduty's

Have you looked at your anti lock braking system. It will give a pulsation when it is in use. You may have a problem with it and it is coming on prematurely. Listen when your truck is doing this and you should hear the humming of the antilock system if it is on. Otherwise i would ckeck your ball joints and tie rod ends for wear as this can cause a vibration back thru your braking system as well

Don't know the USA system but here in Europe the sister car with the same engine does 13 liters per 100 km on city, 9 l / 100 km on road and 12 l / 100 km on highway.

check wheel bearings , loose ball joints steering idler arm...

HAVE THE TIRES BALANCED AND CHECKED FOR SEPARATION