The GP40 is 3 feet (0.914 m) longer than its EMD 567D3A-engined predecessor, the GP35, and distinguished visually by its three 48-inch radiator fans at the rear of the long hood, while the GP35 has two large fans and a smaller one in between. It was built on a 55 ft (16.76 m) frame; the GP35 was built on a 52 ft (15.85 m) frame - as was the GP7, 9, 18, and 30. The difference in length can be seen in the GP40's ten handrail stanchions compared to the GP35's nine.
The GP22ECO is a locomotive built from recycled GP40/GP40-2 parts. The frame, trucks, and carbody are refurbished, while the 16-645 engine is replaced with a new 8-710-ECO engine. The electrical system is replaced with a modern microprocessor-based system. Horsepower is reduced to 2,150 due to the smaller engine.