At nearly two yrs old your dog is old enough to be able to jump out of a vehicle. unless there is some sort of underlying issue. I understand the breeder not wanting a puppy to jump out of a vehicle, but your dog is mature enough to handle that now. If he won't get in the vehicle by himself, I would have his hips checked. (if he is not in pain, forgo the hip check and realize it may be because you have been enabling him to use you) You could try a small step stool. My dog is severely cowhocked and needs help getting into my sportage, up stairs, etc. Since you have been doing this for your dog since a very young age, he has not been able to develop the confidence to do it himself. He knows you will help him. Once they do it for themselves with lots of praise, he will do it again. Step stool to start would be helpful. Hope this helps.