1997 Buick Skylark-power steering

1997 buick skylark/6cyl/3. Something engine, 89,000 miles. Car was making a whining noise when turning the wheel. Had power steering pump replaced. Noise was worse and also groaned. Replaced ps pump again, thinking it was a bad one. Did not help. Pump was replaced again with another brand. Car was still whining and increased pitch when accelerating. Hoses were replaced. Rack and pinion was replaced. Car sounds terrible in (cold ) weather. As a last ditch effort, replaced ps fluid with ATF+4. Car groans and chatters upon a hard left or right, whine is always there. The next step planned is to replace rack and pinion (again). When the weather is warm, there are very little symptoms, except some high pitched whining, but when it is cold outside the car groans terrible when turning the wheel. Any suggestions?My mechanic is stumped.