1999 Pontiac Grand Prix. 3800 v6

Wow, that's a lot of parts to replace when you don't even know what the problem is. I'm guessing the new steering rack was not bled properly, so there is air trapped inside it. But its an old car, so there could be other issues. Sometimes a professional evaluation is worth the money spent. Any competent front end shop should be able to pinpoint the problem if you're having difficulty finding it yourself.