When it was noticed that the 75 mph (121 km/h) class 24 was too slow for many tasks, the 90 mph (145 km/h) class 25 was born. Thanks to an intercooler, the engine now produced 90 hp more. Several manufacturers delivered a total of 327 locomotives of subclasses 25/0 to 25/3, which mainly differed in terms of the electrics. They mainly hauled freight trains, but some locomotives had steam heating for passenger trains. They were called “Rats” because of their widespread use. Regular use ended in 1987. In 1983, three locomotives had been converted into electric train heaters, which were carried on trains and scrapped in 1994. Today a total of 20 class 25 units are being preserved.

In the late thirties, the Rock Island operated the “Rocky Mountain Rocket” train that was separated at Limon, Colorado. A section with only three cars went to Colorado Springs and the operator wanted to get a special locomotive that would blend into the whole train before hauling the shorter section alone. The solution was an E6 B-section with a cab and other equipment needed to lead a train, but with a blunt end to fit into the aerodynamic appearance of the train.

Due to the lower power requirement of the three-car train section, only one 1,000-hp prime mover was installed. The remaining space was taken up by a baggage compartment. The two AB6 were used in this role until 1965. After this, a second engine was installed alongside with a generator that replaced the steam heating boiler. The second, unpowered truck was now also powered. In this configuration, they were used in suburban service in the Chicago area until the mid-seventies.

The TA was a small series of six four-axle diesel-electric passenger locomotives ordered by the Rock Island for their “Rock Island Rocket” trains. They were built at the same time as the EA, E1 and E2, but did not have the middle carrying axle in their bogies and only had a single 16-cylinder 1,200 hp engine. The “T” in the type designation stood for “twelve hundred”.

The six locomotives of the Rock Island carried a livery in maroon, light red and silver. When new rolling stock was introduced for the Rocket trains, the locomotives could still be used on their own and came into local and suburban service. They were finally retired in 1957 and 1958 and scrapped. Although no other customers did order the TA, it can be seen as an important step between the customer-tailored diesel locomotives and the later standard types.

The GP50/SD50 series built from 1980 introduced some technical features which had been tested in the GP40X prototypes. The new HT-B trucks were never used in production, but other features taken over from the GP40X were the new radiator coverings which were called “elephant ears”, and the new “Super Series Wheel Slip Control” that uses a Doppler radar to monitor wheel slip and reduce power when needed. Additionally, they introduced microprocessors into production locomotives.

The GP50 was equipped with an optimized 16-645F3B prime mover that delivered 3,500 or 3,600 hp. With still only 16 cylinders compared to the SD45's 20, the frames could remain as short as in the GP40. New traction motors were introduced which could cope with the increased power being split among only four axles. In total 278 GP50 were produced for five customers, most of which have either been scrapped or rebuilt in the meantime.

The GP49 was a variant with a reduced power of 2,800 hp introduced in 1983. In this case, Alaska Railroad was the only customer with four locomotives built in 1983 and five in 1985. Six GP39X built for the Southern Railway were later rebuilt to GP50. In 2006 Alaska Railroad started to sell their GP50 and two of them went to Ferronor in Chile where they were rebuilt to six axles. The six rebuilt by the Southern Railway were last used by commuter operator Tri-Rail in Florida. There they had been equipped with head-end power.

After the classes KK16 and AA16, the Egyptian National Railways ordered another 70 diesel locomotives from Henschel, which were again built under license from EMD. They were to be used for light passenger service and were therefore designed with a lower weight. The 567 series engine here had twelve cylinders and delivered 1,425 hp. In this case, four axles were enough, all of which were powered. Since high speeds were not used in lighter service, the maximum speed of 100 km/h was even lower than that of the KK16 freight locomotive. With a total length of almost 19 meters, these locomotives were the shortest of their sister series.

After the 13 class KK16 freight locomotives, ENR ordered 38 passenger locomotives from Henschel, which in turn were developed based on EMD technology. In contrast to the predecessors, these locomotives only received an engine from the 567 series from EMD, which here had 16 cylinders and delivered 1,950 hp. One motor reduced the length of the locomotive by about two meters. The three-axle bogies were still equipped with two traction motors and a carrying axle. They were designed for a top speed of 120 km/h and were 20 tonnes lighter than the KK16.