Vibration/Shake at certain speeds

I would have your drive line inspected to make sure there is not a problem with the U-joints. Often the speed related vibration is caused by drive line imbalance. Sometimes it can only be corrected by having the shaft dynamically balanced. Happened on my Ford. It was masked by the bad tires that I blamed for the problem, new tires just made it more distinct.

Inspection and repair are not too bad, but should be done by specialty shop. They have the proper equipment. Seems to me I had a U-joint replaced on my little van for about $60-75. Did not have the balancing done which was $75.