It's been a while since I posted so here is an update. As far as riding in the truck nothing has changed. Believe it or not, since Ford doesn't have anything like ANC, I talked a local dealer into letting me test drive a 150 with the dog along. Her reaction was the same. That being said I was not surprised because her "anxiety" has turned into a full blown psychosis. She is only safe/happy when inside or in our fenced yard. Walks only when she wants to, and still needs to be forced into the truck. When she does walk she's excited to go, but sometimes we only get 10 feet from the door and she locks up. Can't figure it out. A sound or a smell, I don't know. Also, if anything is different - a delivery box in the house for example, she is spooked by it (barks at it, runs from it or approaches it as if it will attack her). It's sometimes comical, but this craziness has become a way of life with her. Because of this I no longer think the truck is the issue, it just may have been the start of her anxiety. Some research shows that this is not uncommon with Jack Russell's. Just a bit hard to understand since she is 4, and her first 3 years she was a normal dog.
So I appreciate all of the help and suggestions you all have offered. I've literally tried everything - including vet recommended anxiety meds (which just seem to dumb her down). I can only hope at some point she will adjust. Or maybe I can get Cesar Milan to make a visit!
Talisman: So sorry to hear about your dog. 19 awesome years with a good old boy - I feel your pain. Despite the issues with my girl, I love her to pieces regardless.