Starting in 1997, Union Pacific took delivery of 21 SD90MACs with 4-cylinder, 6000 HP prime movers. Roughly a decade later finds 20 of these 21 units in storage, not being used. The 21st unit has been returned to EMD for testing purposes. One of the 20 units in storage, UP 8923 (ex-UP 8513) is seen at Burnham in Denver.
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