Unlike the original GP39, which sold only 23 examples as railroads preferred the reliable un-turbocharged GP38, the GP39-2 was reasonably successful, ascribed to its better fuel economy relative to the GP38-2 which became of more interest in the 1970s energy crisis, and to its better performance at altitude.[1]
^Foster, Gerald (1996). A Field Guide to Trains of North America. Houghton Mifflin Field Guides. ISBN0-395-70112-0.