I got an idea of what other kind of passenger train UP might be running, and a took a short break from work to go look. My timing was good.
Sure enough, it was a Union Pacific business train, charging east at full speed in the dramatic lighting shortly after sunrise. I couldn't pan and follow it because I would have ended up pointing the camera right into the sun, which seemed like a bad idea.
Trains like this have very high priority (they usually have important railroad officials on board), so the dispatcher was clearing everything into sidings to make room for it.