Oddly enough, I just drove my 4Runner from SW WV to Dayton to Columbus back to SW WV between yesterday and today. I did notice a little (and by little, it was just enough to notice... I simply let go of my death grip on the wheel for that section of road) vibration on a section from Dayton to Columbus.... and only there. It is entirely possible that certain road types match up with the resonance frequencies of the 4Runner and exasperate an out of round/out of balance condition.
Have you tried finding a seriously smooth patch of road and seeing if the vibration is present? If the vibration is present on a really smooth, nice road, I think you'd have more ammunition that there is a problem. (Good luck finding that in Ohio! :cheers: )
As far as the field technical guys, you must keep in mind that most of them are going to drive the vehicles and do what they can practically do at that time. They could waste everyone's time and money throwing parts at the problem and not understand and, likely, not correct the issue or create some other problem. Most of their work is in data collection. In my past life as a quality engineer, sometimes I'd go to our customer and I'd be able to quickly diagnose an issue and get the repair done. That was pretty rare. Sometimes I'd have to ask if we could do a larger repair and take all the parts back to me so I could do a deep dive on the issue (in your case, that could be a steering rack, bushings, suspension bits, wheels, tires, etc). Other times we'd compile and review the documents that the field techs made and send back requests for every single part replaced for a certain problem and then we'd have 5 or 10 failed parts that we could review side by side comparing build dates, part measurements, witness marks, etc. From what has been posted, the field tech probably drove your car, drove the car off the lot, noted the vibration on both along with tire types, road surface and materials, speeds, etc, and made a complaint document to go back to Japan for the actual design engineers to review. Fully understanding and correcting issues is a very difficult and involved process.
Trust me, we aren't happy when a customer isn't happy with their vehicle. I HATE when a Toyota lets someone down because I have a lot of pride in my company and we want to give you the best product we can. We know that happy customers are repeat customers and we'll do what we can to make the customers happy, but sometimes it takes time to really understand the real root cause behind an issue. Document everything, check out some different road surfaces, and be patient. If you have the documentation in place and Toyota figures out a fix for your condition, corporate is usually very good about making sure it doesn't cost you. Note I said corporate and not the dealer.