As with the first generation, the GP28 and GP35 were once again offered as six-axle variants with the same engine power. The SD35 with 2,500 hp was offered from June 1964 and 360 were built for customers in the USA. 100 of these went to the Southern Railway, followed by 80 for the Norfolk & Western. From July 1965 the SD28 with 1,800 hp was also offered. Since a six-axle locomotive of this power class was apparently not very attractive on the market, only two were sold to the Columbus and Greenville Railway and four to the Reserve Mining Company.
Just one month after the launch of the SD35, the Seaboard Air Line ordered 20 passenger locos to replace their old E-series locos and still be able to be used as freight locos if required. They were based on the SD35 with a steam generator and gear ratio for 95 mph and were designated the SDP35. A total of 15 more were ordered, ten of them by the Union Pacific. When Amtrak took over passenger service, the SDP35s remained with their operators and were used in freight service and shunting. The four pieces of the Louisville & Nashville were even reconfigured before delivery and delivered without a steam generator. A passenger variant of the SD28 also appeared, six of which had been ordered by the South Korean state railway. These were significantly lighter and shorter than the other six-axle locomotives.
