Mine does the same thing. 56,000 miles and it has done it since about 10,000. I've replaced the idler arm x2, lower control arms, new shocks, anti-sway bars, new front springs, new tires, and alignment x 3 to no avail.
Try a search on "wandering screw" and you'll see that many of us have the same problem. I thought it was an early production problem with the steering gearbox/pitman/idler arms. My screw is an early '01, Built 6/00 and most of the other posts seem to be from '01 owners. I would suggest pressing the matter with your dealer in case it is something other than what we think was an early design flaw.