There's also the transit of the Rockies, and the tunnels associated with it. According to Bob Krieger, it's Not Fun - I used to have a CIS posting from him about bringing both 844 and 3985 out to the West Coast; the diesel was third in line, and choked on the "air" it was trying to breathe while climbing in a long tunnel, and they had to open up both the steamers to get out of there. (The crews had breathing gear, but the locos didn't.)