Couple of points I know for a fact, that SP allowed the #4449 to run alone without assistant except in regular "helper territory" Donner, Tehacapai, Cuesta, Dunsmuir, Pengra Pass. Out of helper territory, diesels were removed. If anyone remember the AFT, the #4449 ran along except in helper territory. IN May of 1999, UP ran the #844/3985 west to the dedication of the new Roseville yard with a 22 car train. UP had a singe AC44 BEHIND the Steamers and as soon as it got inside the Big Hole, it died leaving the two steamers to crawl up the 2.4% grade by themselves. I was on the train and when the train stopped for servicing at Norden, Steve Lee commented to me that another 30 seconds inside the tunnel could have been fatal because of the heat and smoke. Mr. Lee said he had a new appreciated for Cab-Forwards! Doyle McCormick uses the diesel to save water and give the #4449 a boost when leaving a siding. Hopes this help, Juppo, Good question!