Does anyone have the years and numbering series for when the SP did capital rebuild programs on their GP and SD diesels? When they added a suffix such as "E"?
it's actually quite simple, the rebuilt E's (GP9E) were rebuilt locos "sold" to the Southern Pacific Equipment Company and leased back to the Southern Pacific Railroading, This company was merged into the railroad in January 1977, and the E was replaced with the R for a rebuild
See if these links have the info you are seeking: https://utahrails.net/sp/sp-r8-grip.php https://utahrails.net/pdf/SP-Grip-Program_CTC-Board_Oct-1985.pdf