unstable at freeway speeds

Back up a minute - what do you think about your tires themselves? Tires and air pressure are probably the number one cause of unstable road feel and wander. I would really look at the tires closely and then go from there. On the alignment - I would acquire the specification sheet - before and after the alignment from the place that did it. This will prove whether the alignment was previously out of specification, and if it currently is in specification.