More than likely the guys above are correct in it being a tire issue as the MPH's you listed are in exact line with this issue. Have you examined all 4 tires to see if any one tire has more tire weights than the other? This is often an easy way to spot a bad tire that they had to spin up multiple times to balance. If your steering wheel is shaking I would check the front to and if your rear end is getting a nice massage I would check the rears.
If any one tire is messed up and you bought them from a major tire dealer consider taking the car to another shop in the chain to have them examine it. I've had bad tires before and the difference can be the dealership when it comes to repair/replacement.
If any one tire is messed up and you bought them from a major tire dealer consider taking the car to another shop in the chain to have them examine it. I've had bad tires before and the difference can be the dealership when it comes to repair/replacement.