Shimmy

I had my tires rotated about a month and a half ago and since then my truck has had a vibration whenever I drive at speeds faster than 60mph. I have had the tires checked for defects and they are all good. My front wheels have had to be rebalanced everytime that I have taken the truck back to the tire store that rotates the tires. Is it safe to assume that I need new wheels?

reverse them, back to front, front to back. see if it goes away.

it’s possible that the tires got worn when they were on the back. any abnormal tire wear?

How were they checked for defects?

Have them spun on a Road Force Balance machine. That spins the wheel while pressing a drum against the tread to simulate road forces. It can detect suttle conditions and/or defects better than regular machines.