Humm your making me think about the R & R of the steering Box now yes they could have messed that up somehow perhaps
About the Wheel Balance , was that done right on the Car or on a off the car Balance machine :
Why ? : Because if their are any issues Tire wise or wheel wise , weird Bearing's or installed wrong all of that will show up with a " On the Car " Balance machine "
I would make sure to mention the speed as most operator's don't spin the Wheels that fast more like 60 MPH Max

As well you mention the Motor Mounts : Moving them to a New Height could in fact change something . Should be to the better but those are the things that have changes
something to ponder . The up and Down Movement is very unusual ? that's why I mentioned to look for any Frame Cracks / Damage ..
Yes I missed the new wheel Bearing install sorry about that . Something is not right that's for sure