For folks who are new - this issue has been around since the 5th gen - really in some sense since the 3rd gen. There are a billion threads about this and how different people have resolved it. Toyota calls the condition "steering wheel flutter". The solution for the Lexus GX models was a firmer preload spring in the steering rack control valve that increases the rack's internal resistance to feedback - (think of it like adding a firmer steering dampener). it also applied to the Fj Cruiser and maybe the 4Runner for some years.

https://static.nhtsa.gov/odi/tsbs/20...31942-9999.pdf

If you can do this in 4hrs - I'm impressed!

"Some vehicles may exhibit a steering flutter condition while driven at approximately 55 – 70 mph. In some cases, this concern is caused by a wheel imbalance or RFV (Radial Force Variation) that is out of range. If the tire and wheel assembly is satisfactory, a steering control valve preload spring is available to reduce the steering flutter felt through the steering wheel."