When Frederic C. Dumaine became President of the D&H in 1967, one of his high priorities was to upgrade the remaining passenger service. The PA1's were refurbished and repainted in a Santa Fe-like paint scheme, and used with ex-Rio Grande Budd stainless steel passenger cars on the daily New York-Albany "Laurentian" and "Montreal Limited" trains. In addition to the four AT&SF PA1's, the D&H also acquired an ex-New Haven PA (#0783) for spare parts. For a while, the locomotives were well cared for, but came to an end when D&H was taken over (by court order, along with the E-L) by the N&W at the inception of the Penn-Central merger. When Amtrak took over most rail passenger service, the D&H trains were not included, and the PA's were out of work. Two (17 & 19) were traded to GE. However, Hurricane Agnes in the summer of 1972 destroyed much of the neighbor Erie-Lackawanna, rendering the court order null and void. New management was brought in, and the new D&H President, C. Bruce Sterzing, re-acquired the two PA's from GE. The 244 prime movers powering the PA's were worn out, but the D&H managed to get three of them operable, and convinced the State of New York to use the D&H equipment on a partial state-sponsored restoration of the New York-Montreal train service in cooperation with Amtrak. The D&H was in need of reliable passenger locomotives, and in a joint project with Morrison-Knudsen, the Model 244 prime movers were removed from 16 and 19, and the bodies were shipped to Boise, Idaho in June 1974 for installation of Model 251F prime movers. The returnig locomotives were classed as PA4's, a model never produced by Alco. After returning to the D&H, its attended assignment was taken over by Amtrak's Turboliners, and it was sold to a dealer (along with the other three PA4's), who sold them to FNM in Mexico. It was wrecked, and stored, later purchased by Dolye McCormack, to be cosmetically restored for display at the Smithsonian.

The D&H ordered nine C628 units built in the Spring of 1964, followed by nine more a year later. The D&H C628's, No. 601-618, were the Railroad's first big power and were used system-wide for about 15 years. In their later years on the D&H, they were commonly seen on the run-through trains established with the Lehigh Valley, NE-87 and NE-84, which provided expedited service between the South and New England. The C628's of both railroads put on impressive shows on the steep grades encountered on this route. By the mid-1970's, the D&H, which had been committed to six-axle power, underwent a change of policy in favor of four-axle power. This, and the Railroad's deteriorated financial condition, resulted in the acquisition of second-hand four-axle power and the disposition of virtually all of its six-axle locomotives. In 1978 the C628's were sold to Diesel Supply International, and they were leased to the National Railways of Mexico, operating there until the late-1990's. Arguably the Delaware & Hudson was historically Alco's most faithful customer, and the C628's marked the Railroad's last purchase of locomotives from Alco. However, in no sense did this fact end the D&H's acquisition of products of Alco. Among the D&H's second-hand acquisitions were the former Lehigh Valley C420's, obtained at the formation of Conrail, and later, Conrail C424's and a C420.

The RF-16 was the successor to the DR-4-4-1500, Baldwin’s challenge to the Alco FA-1/FA-2, EMD’s F-3/F-7, and F-M’s CFA-16-4. It produced 1600 hp (actually 1750 hp, but listed in the sales literature as 1600) from a Model 608A 8-cylinder inline prime mover, Westinghouse 471 main generator and 370 series traction motors, and an infinite-position air throttle. The electrical wiring was run in conduit pipes on the opposite side of the carbody as the cooling pipes, to solve the problems experienced with wet electrical equipment in the DR-4-4-1500. It was dubbed “the Hauling Fool” in Baldwin sales literature. The final count was 160 units produced.

In 1973 the Green Bay & Western embarked on a program to upgrade and remanufacture its remaining fleet of locomotives equipped with Alco Model 244 engines – four RS-2’s and four RS-3’s. The approach taken was the brainchild of GB&W’s Norwood Shops Diesel Supervisor Ralph Stuteen. He reviewed a program undertaken by the Portuguese Railways to re-engine their fleet of RSC-2’s and RSC-3’s with Model 251C’s. Since the 12-cylinder Model 251 engine was longer than the 12-cylinder Model 244 due to the 251’s greater width of crankshaft bearings, Stuteen concluded that the slightly shorter long hood of the RS-2 would not permit shoehorning of a Model 251 into it without major modification, and the RS-2’s became recipients of hand-me-down components (from the RS-3’s) in the GB&W program. The re-built RS-3’s were designated RS-20’s due to the 2000 hp produced by the Model 251C. The GB&W’s RS-20 program was highly successful, and attracted the interest of other Alco-committed railroads and of locomotive builder Morrison-Knudsen of Boise, Idaho. Morrison-Knudsen used the GB&W RS-20 program as a template to market the remanufacture of RS-3’s which were still being operated in significant numbers but were otherwise nearing retirement age. The RS-3’s remanufactured were designated as TE 56-4A by M-K, and also incorporated the 12-cylinder Model 251C rated at 2000 horsepower. Additional new major components included radiators and cooling fan, lube oil cooler, an AAR-Type control stand, and 26L air brake equipment. The rear belt-driven traction motor blower was eliminated, and cooling air was ducted from a higher capacity front blower to provide cooling for the rear traction motors. The tip-off to this feature is a flat duct mounted on top of the long hood running board on the locomotive’s left side. In lowering the short hood, this end became the front of the locomotive. The remainder of the major components were rebuilt, and the locomotive was completely rewired. After M-K completed a pair of modified TE 56-4A specification (1800 hp) units for the Detroit & Mackinac on August 20, 1975, the company undertook a far more ambitious TE 56-4A effort, the remanufacture of eight RS-3’s for the D&H. Up to that point, the D&H had been working on a design of its own, and had gone so far as to complete a locomotive superstructure at its Colonie Shops. At that point the project was abandoned in favor of shipping 10 RS-3’s to M-K for TE 56-4A remanufacture. Like almost all of D&H’s large roster of RS-3’s, these units were dynamic brake equipped, a feature the D&H wished to retain on the remanufactured units. The original short hood formerly contained the dynamic brake assembly, and with the short hood being cut down to “low-nose” configuration, the dynamic brake had to be repositioned. So M-K designed a box to contain the resistor grid and blower assembly and mounted it on the top of the long hood above the generator (just behind the cab). To provide room for additional equipment and improved cooling for the 2000 hp Model 251C engine, the long hood was increased in height by 6½ inches. The first D&H unit (#501) was completed on December 13, 1975, followed by three more by the end of the year, and the final four in early 1976. Number 506 came from M-K as #1976, in a Bicentennial red-white-blue adaption of the D&H’s “lightning-stripe” scheme. Remanufactured RS-3’s are typically referred to as RS-3u’s. A number of other railroads performed more modest modifications of RS-3’s, primarily in adopting the low-nose configuration.