This does sound like a power steering issue, as the pump should still work at low speeds. In park with the engine running, I see a slight drop in rpms when I move the steering round a bit and I can feel the pump kick in.
I don't recall seeing it in the owner's manual, but I change the power steering fluid every 2 years on all my cars. I did it right after buying the RA used, and knock on wood, no issues.
For joint issues, I've had good results with glucosamine with msm. I'm popping that stuff like candy