I agree that it is usually tires.

But if that doesn't fix it, check the driveline again. You cannot really check U-joints without removing the driveline. And sometimes the balance just goes sour for no apparent reason. That is when you take the whole shaft to a driveline shop and have it rebuilt and balanced.

You might be able to tell a problem with tires from a problem with running gear. If you can feel anything in the steering wheel, it is probably something in the front end, including front tires. If you feel it in the seat of your pants and the soles of your feet, it is probably running gear. But admittedly, often you just cannot tell by feel.