Rack and Pinion replacement?
 

I have a 2007 es350 with 166k. Some vibration felt between 40 - 45 mph. Mechanic says I need to replace rack and pinion at a cost of $2k. Just can’t justify right now but I did put on 4 new tires. Is this something I should be okay driving with?

Did your mechanic say specifically what was wrong? Rack & pinion replacement is quite a major piece of work.
$2k sounds about right as most of it will be labour.

I bet there is nothing wrong with your power steering rack. I suspect it is all either bad balancing of your new tires or you have a defective tire. Take it to where you got them (I hope it is not the same place as the guy who wants to sell you a rack & pinion to make his boat payment this month), and complain. Defective new tires and crappy balance jobs are not uncommon, as are wheel weights falling off.

If not leaking fluid, do a drain and fill of the power steering reservoir. You can do this yourself. The whole system only holds about a quart.
A Turkey Baster will easily remove most fluid. It takes Dexron 3 Automatic Transmission Fluid which is no longer made so get Dexron 6 instead. You only need 1 quart. Put in new fluid and drive for a day then repeat the process and pay attention if the vibration improves.

If it does not get better, and it is not your tires, go for a second opinion on the cause. Don't say this guy says I need a steering rack, just say you have a vibration. There are other more likely causes than the steering rack that are much cheaper to repair such as bad ball joints or tie rod ends etc.or even a bent wheel.

Balancing, defective tire or a bad driveshaft. The R&P has nothing to do with the vibrations.

Well...I held off the R&P replacement but I did put on 4 new tires. Still have the vibration 40-45 MPH. Could it need a front end alignment?

Alignment does not cure vibrations. If the person doing the alignment is diligent and inspects everything (which is rare) they may find your vibration problem.

However I am confused about your timeline from your original post wording.
Did you mean you had a vibration then put on 4 tires and still have it. Or did you mean that you put on 4 tires and then had a vibration?

If the vibrations was there before the new tires then you need a different shop to inspect the front end components, including axles, motor mounts, transmission mounts, wheels etc for wear and defects that could cause the vibration.

If the vibrations began with the new tires see my earlier post and take it back to where you purchased them. I have purchased new defective tires from Tire Rack that they accepted for return after the installer told them they could not be balanced to stop a vibration similar to yours.

If you need help finding another shop use this link to begin your search. https://www.cartalk.com/mechanics-files

I put on new tires and it did not fix the vibration. I'm beginning to think the shop doesn't know what they are doing

Don't go back there. Get a second and maybe a third opinion. Use the link I posted above to begin your shop search as it lets you search by city and state. Then cross check a potential shop on Google and Yelp.
Let us know what is found to be the source of the vibrations.