 Although the GP40-2 was a sales success, it sold fewer units than the earlier GP40 and the contemporary GP38-2 and SD40-2 models.The popularity of high-horsepower 4-axle diesels began to decline with the GP40-2, with 6-axle models gaining in popularity for their superior low-speed lugging performance.Like the SD40-2 the GP40-2 has a reputation for reliability, and many are still in use.