Electro-Motive Division built this locomotive as a SD40 test bed in early 1965. The Union Pacific Railroad lists this locomotive as a SD40X. It is built on an SD35 platform with oversized flared radiators. It originally served as an EMD demonstrator and was sold to Union Pacific in April 1966. A total of eight of these locomotives were built, and according to Trains Magazine only two still survive: this locomotive and former UP 3041 (now MKCX 9051).
This SD40X shouldn't be confused with the later SD40X's which were developmental SD50's built in September 1979 and sold to Kansas City Southern.
Sources of Information:
Trains Magazine, Kalmbach Publishing Co., September 1997, pp. 55 - 65.