Core units for the GP10 program were from IC/ICG GP7, GP8, GP9 and GP18, B&M GP9, B&O GP9, CRR GP9, C&O GP7 and GP9, D&RGW GP9, DT&I GP7 and GP9, FEC GP9, GTW GP18, P&LE GP7, Potlach Forests Inc. GP7, QNS&L GP9, RDG GP7, St.J&LC GP9, SLSF GP7, SP GP9, SSW GP7, and UP GP9B.

Nine Alaska Railroad GP7s were rebuilt to GP10s by Paducah, and renumbered 1801-1809 (these rebuilds received EMD angled cabs but kept their AAR Type B road trucks from Alco RS-1s).

The 1978–79 Conrail GP9 rebuilding program by Paducah was engine and electrical gear only with no carbody modification (the high short hoods were kept).

The Precision National Corporation Shops at Mount Vernon, Illinois rebuilt six Conrail GP9s to GP10s in 1978.

The GP9 rebuilding program by Boise was engine and electrical gear only with no carbody modification.