[Beav]

There's a variety of things that can cause 'yaw', dually tire ruts are the most common, as a car's track rarely fits them. As the tires track in and out of them the car becomes unsettled. Another possibility is 'creeping' the kind of sick, small swerve to one side and then back when changing lanes. It's caused by tires and some tire/car combinations. Sometimes inflation adjustment will help. Some roads were paved/repaved with the lane seams close to the normal tire path and make this more noticeable.

Have you tried rotating your tires, straight front to back? You may have the beginnings of a tire separation. I'm assuming all four tires are the same manufacturer and size and tread wear.

If this doesn't point you in the right direction, let me know and I'll give you some more ideas.