I was always taught that the power steering fluid should be changed approximately every four years or 50,000 miles which ever comes first! Why? The fluid is not filtered and is subject to the atmosphere and over time it will beak down. The fluid reservoir is not a close system! I am surprise it is not required by Dodge/Ram for our trucks to be changed!
I am just old school and I do change the fluid in the power steering and brake reservoir about every four to five years.
I have replaced both of my u-joints and steering ball joints on my current truck along with other vehicles such as Jeeps. An I never have had hard steering input or resistance from these components. But I did get what some call the Death Wobble and have failed steering Stabilizers do to the failed components of the ball joints and u-joints. That's why I lean to the dirty fluid in the power steering pump as the cause of the steering resistance.
This is easier to change and cheaper than anything else on the truck, to replace. I would do what is easy and cheap to do first and go from there.