Shimmy at highway speeds

Is this something that you feel in the steering wheel or in the seat?

https://www.2carpros.com/articles/steering-wheel-shakes-when-accelerating-or-braking

Depending on which you have will determine if this is in the front or rear.

Also, when you had the tires balanced, was there any wear to them? You can check the tires now to see if they are worn with the chart attached below.

Also, were the tires road forced balanced or just balanced?

If we can eliminate the tires, then the next likely cause is hub or rotor runout. This will require a dial indicator. However, we can get there once we know this info. Thanks