The Illinois Central Railroad had three separate rebuild programs to upgrade their old EMD GPs and GPs that they had purchased from equipment dealers such as Precision National Corporation in Mount Vernon, Illinois. The first was the GP8, second the GP10 and third the GP11. All were rebuilt at IC/ICG's Paducah Shops in Kentucky.
Two IC GP9s were rebuilt to GP10s and sold directly to the Ashley, Drew and Northern Railway. Nine Alaska Railroad GP7s were rebuilt to GP10s by Paducah. A total of 76 Conrail GP9s were rebuilt to GP10s. The Paducah Shops rebuilt 53 Conrail GP9s to GP10s. The first 16 Conrail GP9s were rebuilt to the equivalent of a GP10 in 1976. In 1978 another 21 Conrail GP9s were rebuilt at Paducah, followed by 16 more GP9s rebuilt to GP10 in 1979. The 1978–79 Conrail GP9 rebuilding program by Paducah was engine and electrical gear only with no carbody modification. The Precision National Corporation Shops at Mount Vernon, Illinois rebuilt six Conrail GP9s to GP10s in 1978. The Morrison-Knudsen Boise Shops rebuilt 17 Conrail GP9s to GP10s in 1978-1979. Six units were rebuilt by Boise in 1978, with an additional 11 units completed in 1979. The GP9 rebuilding program by Boise was engine and electrical gear only with no carbody modification.