The City of Denver and the Denver Zephyr ran on nearly identical 14-1/2 hour schedules and were the preferred trains between Denver and Chicago. The Rocky Mountain Rocket ran on a slower, 17-1/2 hour schedule between the two cities. For this reason it's probable that the majority of the Rockets Denver passengers were going to/from the intermediate cities it served, Omaha excepted. The UP's faster City of Denver would have been preferred by Omaha Passengers.
On the other hand the Rocket was the only through train between Colorado Springs and points east so it would have been the train of choice between that city and even Chicago.