Out of round usually will only cause a vibration when braking. Its easy to detect by applying just the emergency brake. If it pulses when stopping, then the drums need attention.
But, if you feel it while not braking, then you need to check everything else first. It sounds like you already have, but be sure to rotate tires and rims, not just change tires.
Most brake drums are balanced from the factory. You can usually see the weights welded on the outside.
If you see a place with the remains of spot welds and a mark, then one of the weights may have come off.
Another consideration, wheel bearings will sometimes cause vibrations when going bad.
A trick nobody seems to think of, is to simply drive down a four lane or a deserted two lane with someone following you.
You really need two people in the second car. One to drive and one to watch. But they can come up alongside you and watch the wheels.
Then move over and have them do the same on the other side.
If you have much of a vibration, it will be visible. That at least lets you narrow it down to which wheel.
