By the mid 50s, increasing pressure from long-haul trucks, declining passenger revenues and mounting costs forced railroads to find new ways to improve service. Faced with expensive overhauls of early cab and hood unit diesels, many began looking at new equipment as well as ways to improve existing motive power. In 1955 Union Pacific equipped several GP9s with turbochargers as an experiment. Their success inspired EMD to create its own turbocharger for the 567 prime mover resulting in a 2,000 horsepower locomotive designated GP20. EMD offered to rebuild older FT units into new GP20 locomotives using remanufactured parts from aging FTs. This allowed railroads to trade in four FTs totaling 5,400 h.p. for three new locomotives providing 6,000 h.p. All the remanufactured parts carried a new factory warranty. Many railroads took advantage of this cost saving program.
Early in their careers, the new units were typically assigned priority freights that demanded higher speeds. With the arrival of newer power, they were gradually bumped into secondary runs, and eventually spent their last years in local and yard service. Following their retirement, a few went to work for shortline operators. Western Pacific #2001, the very first GP20, was donated by UP to the Feather River Rail Society in 1985, where it has been restored to its as-built appearance.