I did take a BMW 528e from Alberta to Colorado back in 1983 on a re-location move for a company. I had no trouble registering it and in fact, selling it down there. That was 23 years ago and I do forget the paper work required but it was not much IIRC. The car was part of "settlers effects" ie. possessions taken on the move that were owned prior to the move. Sorry, this is not much help.