For the second half of the 1998 production year Cummins made some major mechanical changes to the 2nd generation Cummins-powered trucks. These trucks would maintain their signature body styles but would be powered by a modified version of the 5.9L Cummins engine. Improving horsepower and torque is always one of the main objectives for competing diesel engine manufacturers, which influenced the production of the 24 valve 5.9L Cummins. One key upgrade to the 5.9L Cummins was doubling the number of valves in the cylinder head to 4 valves per cylinder. The combination of increased valves and an enhanced fuel system would significantly increase airflow, and provide more precise fueling, all while delivering more horsepower and torque. Paired with the new 24 valve Cummins engine were new drivetrain components to further improve overall performance.

Maintaining durability was another major focus when redesigning the 5.9L Cummins. The cast-iron block and cylinder head proved they could handle increased power. Utilizing 4 valves per cylinder gave the 5.9L Cummins enhanced throttle response and a broader torque curve. The upgraded cast-iron 24 valve cylinder head significantly improved coolant flow in the engine. The forged-steel crankshaft and connecting rods were carried over from the 12 valve Cummins engine due to their durability and longevity. To increase performance components in the fuel system were upgraded. The mechanical injection pump was replaced with a Bosch VP44 electronic pump. With an integrated ECU the Bosch VP44 injection pump pressurizes fuel, controls injection timing, and monitors fuel flow. While the injection pump on the 24 valve Cummins is electric, the injectors remained mechanical. These high-pressure mechanical injectors were redesigned to inject fuel into the center of the piston. With the new centrally located fuel injectors, the cast-aluminum pistons fuel bowls were redesigned to match the injector’s new spray pattern. The 24 valve 5.9L Cummins continued to utilize the Holset HX35W turbocharger on all manual trucks up to 2002 and all 2001-2002 automatic trucks utilized an HY35W turbocharger.