Vibration around 53 mph?

A bit of a dilemma. Car has only 85,000 and is clean, new tires, no play in the wheels, vibrates around 52-65k. Checked balance they balanced them but said 2 of the wheels are maybe bent.I doubted their machine so I put another set of wheels from another c I have, same thing. It almost feels like the cabin vibration you would feel when you have a bad transmission mount. But when you put it in gear while parked you barely get any vibration, so I removed the mount and it's in good shape, same for the center support bearing, anything you suggest I check that I have not thought of? It's an RWD, no AWD.