Since 1960 it ran hundreds and thousands of miles as the Union Pacific's publicity locomotive. From that year to the present, it pulled the Cheyenne Frontier Days from Cheyenne to Denver, CO and back until 2019 when it was decided not to do the Cheyenne Frontier Days Train anymore. It appeared in Expo '74 in Spokane, WA and in1978 went to Ogden, UT for the dedication of the Utah State Railroad Museum. In 1981 it went to Sacramento, CA for the opening of the California State Railroad Museum in that same year it was joined by Challenger 3985 after its restoration. In 1984 the locomotive traveled to New Orleans, Louisiana for the 1984 World's Fair. In 1987 the UP steam team painted the engine in a two tone gray paint scheme. In 1989 it traveled to Los Angeles for the 50th anniversary of the Los Angeles Union Passenger Terminal, where it performed a side-by-side with Southern Pacific 4449. The two engines raced each other up Cajon Pass on Southern Pacific and Santa FE's tracks. On February 14, 1975 it pulled Amtrak's San Francisco Zephyr with a pair of EMD SDP40FS from Denver, Colorado to Cheyenne, Wyoming. On the weekend of October 14, 1990 the engine led a procession of special trains from Kansas City Union Station to Abilene, Kansas where the celebration takes place for the 100th birthday of Dwight D Eisenhower to haul WWll veterans to the celebration. The special train was called "The Eisenhower Centennial Special." In 1991 the 844 and 3985 returned to Sacramento, California for Railfair 91. After Railfair 91 the 844 went to Nebraska to pull some excursions out of Omaha and Grand Island, Nebraska. In 1992 the locomotive went on a major overhaul which went from 1992 to 1996. In 1999 the locomotive and 3985 return once again traveled to Sacramento, California for Railfair 99. The locomotive suffered a tube failure while on display, after returning from California the decision was to redo the firebox structure and cab which the locomotive was out of service from 1999-2005. In 2007 the 844 joined Southern Pacific 4449 for the "Puget Sound Excursion." In 2012 the engine is used to celebrate the 150th anniversary of the Union Pacific Railroad (1862-2012) and it went to Sacramento, California, which the California State Railroad Museum hosted the UP 150 celebration and during the event the locomotive's tender derailed on a tightly curved track from the mainline to the museum. In 2013 the locomotive is taken out of service for boiler work to have a change in water treatment that same year the bolts that hold the Mars Light which was installed in 1946 were failing so the Mars Light had to be removed. The overhaul of the locomotive went from 2014-2016. On June 16, 2016 the locomotive was test fired and completed on June 17, 2016. In July it pulled the Cheyenne Frontier Days Train on the usual way. In October 2016 the engine pulled the "Trek to Tennessee" to Tennessee. This is the first major trip for the newly restored locomotive. In April 2017, No. 844 made its first run on the
Oregon Short Line Railroad to celebrate the 92nd anniversary of the
Boise Union Pacific Depot. Because of heavy snows and a wet spring the trip was cut short and the engine had to run light across the
Malad River because of a washed out bridge. On July 22, 2018, the 844 was involved in a fatal pedestrian accident in Henderson, Colorado. The engine was leading the Cheyenne Frontier Days Special, which carries people to and from Denver and Cheyenne each year for the festival. The train was on its way to Denver when the pedestrian was hit. The train was stopped immediately following the accident. Police reported that the victim was trying to take photos of the train while standing too close to the tracks before she was hit. In December 2018, Union Pacific requested from the
Federal Railroad Administration (FRA) waivers to exempt UP No. 844, 3985 and 4014 from federal
Positive Train Control (PTC) requirements in February 2019, the FRA officials responded that such waivers were not needed. On May 4, 2019, No. 844 participated in the inaugural run of the newly-restored Big Boy No. 4014. The train departed the historic
Cheyenne Depot following a christening ceremony for No. 4014. The two locomotives arrived at the
Ogden Union Station on May 9 for the city's Heritage Festival. The two locomotives were on display at the station until May 12, when the return trip to Cheyenne began. They arrived at Cheyenne on May 19, concluding the first run of No. 4014 in excursion service.