My 2001 2500 2wd is starting to wander. I continually have to steer right then left to hold it straight down the road.  Had it into my alignment shop. All specs are ok. I thought about adding caster, but at spec 3 1/2 degree positive already they said that was enough. I am used to 1.5 to 2 degree with the dana 4wd axle. As I said this is 2wd and all  front end components except steering box  have under 25 k miles on them. Steering sector box? Truck has 175 k on it and I live 1 mile down a washboard road.

If it has the original steering box and if it hasn't seen periodic adjustments, more than likely the box is getting worn. 

Take a real hard look at the control arm bushings because they can be deceiving.  Jack it up and move them  every direction with a pry bar looking for excessive movement I know I've been fooled more than once. 

Lastly have the alignment shop max out the caster adjustments. You should be able the get 6-7 degrees out of it. There is a special tool involved for caster adjustments on a 2wd that not every shop has. 

I've had to re-adjust my steering box a few times. Eventually I'll have to pull my box and do both the sector and bearing pre-load adjustment of the box. All listed in the FSM. Also if the is wear occurring and the fluid is dark colored its time to flush the system out.

Had the alignment shop go to 5 degree pos. They said I had the steering box set to tight.  What is the procedure for adjusting the box?