Remove and rebalance the tires. Sometimes weights get knocked off , or the tire gets spun on the wheel.
Crawl around and look for wheel weights. I bet you are missing some.
If they are using "hammer on" banana shaped weights that go on the outer lip of the wheel, it only takes one light brush against a curb to either slide it around to another position, or more likely, pop it completely off.
My wife used to do this on my '07 all the time. So I would have to ask the tire shop to specifically use the "Stick On" weight squares that go on the flat part of the wheel around the brake rotors where they couldn't get knocked off. They look better that way too.
Even a good tire tech sometimes misses the mark, and with these big tires, it only takes a little bit to create a vibe in a certain speed range - exactly as you describe.
Don't be shy. Have them pop the fronts off and double check the balance.
They should do it for free. I've had to do this many times as I am a perfectionist when it comes to these sorts of things.
