The third of NYC's four classes of 4-8-2s, called “Mohawks” there, was the L-3. In contrast to its predecessors, it was not only intended to pull freight trains, but also passenger trains. An L-2d had already been modified accordingly for testing. The driver diameter was left at 69 inches and the decision was made not to use a second trailing axle in view of the existing infrastructure.

The differences between the L-3 and the L-2 included higher boiler pressure, smaller cylinders and several improvements to the running gear. In the case of the running gear, this included improving the counterbalancing, designing many rotating parts in lightweight construction and mounting the axles in roller bearings. The L-3b and c subclasses were equipped with a booster on the trailing axle. 

Of a total of 65 locomotives, 35 were actually built for mixed traffic and 30 only for freight traffic, which only had plain bearings on the driving axles. The large six-axle tenders had an exceptionally large coal capacity of 43 short tons. The water capacity, on the other hand, was relatively moderate at 15,500 gallons, but the New York Central had water troughs for refilling while running. In this way, large distances could be covered without stopping.

With the driver diameter of 69 inches, speeds of more than 80 mph could be achieved. However, the wheelbase was chosen in such a way that wheels of up to 72 inches could also be fitted. This was only applied to number 3000, which served as a prototype for the L-4.