Re: Colombian 4-8-2 vs K-28 . . . when?

The Rio Grande liked dual-service locomotives, locomotives that could haul both passengers and freight. There were times that the eastbound freight train was held at Durango until after the passenger train arrived so that the passenger engine could be used as the Falfa helper. After helping the freight train and backing back to Durango it would be ready for the eastbound San Juan the next day.
The Chama Cumbres stretch would also have killed the idea of a high drivered engine. Why use two engines when you get by with one. The railroad could have kept the pacific on the Chama-Durango section but the bean counters would not have liked that.