Not sure what you can do short of checking the front end to make sure none of the ball joints, or control arms are worn out. The rack and pinion is not adjustable like the old vehicles with the steering box. You could adjust them with the bolt and lock nut on top, but thus is not the case with the rack and pinion. Take it to a good front end shop and let them check it out to be safe.
Do you have huge offroad tires? If so I did the same issues until I installed a dual steering stabilizer... Some people say they mask problems, I dont get it, I have stuck them on brand new lifted vehicles and they make a world of a difference..