When facing a threat, calling 911 should NOT be your first thought or action (and this situation well-proved that, with no cops responding). Dealing with the threat is the first priority. If you can do both simultaneously, that's good.My only concern is why you didnt call the police right away, instead of talking about what to do, slowing down, grabbing your gun, then deciding to call.
At least your ok.
Keeping in mind Scooby and his buddy had a perfect right to be where they were, in hindsight, turning off on an exit would have been a good tactic -- assuming the other car didn't follow -- but since it was an interstate highway, not sure how plentiful exits are between D and Ft W.
I especially would have worked hard to not come to a stop in traffic with the other car, to the extend I would have done something mildly illegal to do so -- e.g. drive across a sidewalk or median, for example.
Glad you made it thru intact.