https://railfan.com/promontory-nrhs-cha ... re-mk50-3/
These units were built new by Morrison-Knudsen in 1995, and originally had an (unreliable) Caterpillar engine and Kato main generator, later to be replaced by an EMD 645 and main generator when sold to Utah Railroad. I recall when these were delivered the mayor of Denver was at the unveiling, praising the first production 5000HP diesel locomotives. However, DC was outdated for high horsepower by then and it was joked that, because of their DC traction system and wheel slip control, that these units would slip coming out of the sandhouse. Incidentally, back in the days when you could (discretely and safely) climb onto an engine without getting arrested, I was in the cab of one of these being used as a swing helper on the Moffat Tunnel route around 1996, I recall that the cab hopped up and down as it idled. Steven Vincent photo of SP 503.