Slow..Rider,
I usually get into trouble with front end advice, but what the hay! Not many things on the front end would get 'arthritis' from sitting awhile, so my first thought would be old Nylon bias tires.
Zero toe-in could aggravate wander, as well as too little positives caster. Neither of these would develop after the truck sat for a spell...they would be constants.
Maybe you could raise the front end of the truck and check for any binding in the steering box or various joints. You indicated the king pins were new, but check them, and give everything a couple of shots of grease.
If everything is free and not binding, I think the alignment shop might not be a bad place to visit.
Make sure you have lube in your steering box too...old ones tend to leak after years of working and it might be dry and in need of adjustment.
Stuart
