When driving at more than 50 mph, the car seems to be jumping up and down at a rapid pace - all the tires are new and balanced - there is no noticeable alignment issue - the car goes straight on straight roads 
What could be the issue with this car?
The front struts are no good. You can test this by having a heavy person press down on the corner of the front fenders. If the struts are okay, the car should rise and stop almost at once. If they are defective, the car will continue to move up and down a few times. If this is a small or even mid-size car, the cycle of up and down motion while driving at higher speeds could very well be rapid enough to seem like a vibration.
BTW they may not bounce and they still could be bad.