The factory bushings are designed purposely for some rack movement. Why exactly? I don't know but I'm sure there is a reason and because I don't think the whiteline poly bushing creator is smarter than a Toyota engineer, I stuck to the factory setup on my 2000. Why was the rack redesigned for later models? I don't know that answer either but a lot of other things changed too. You could speculate all day about these things. My best guess is that it is designed that way for isolation. With poly bushings, you will probably get feedback at the wheel from the AWD system. The steering system feel on these is already very sensitive to even the slightest tire, wheel, or balance issue.
I posted about it here
If an alignment shop is telling you something is wrong because the rack is moving a bit, it's because they've never worked on a 100 series before or aren't very experienced.
If you have a ticking manifold on the driver side, it would be a great time to replace it while the steering shaft is out.
If I jack the truck up at front driver side, hold the tire in arms and try to move it back and forth, how much play would be considered safe and won't cause long term damage? Or does it have to be very tight with very little wiggling. (Assuming bearing and knuckle are in great condition. Just movement from the steering parts.)