The real takeaway on the 2024 Duramax L5P isn’t the advertised 975 lb-ft. On a 10-speed truck at wide-open throttle, the transmission backshifts before the engine ever gets down to the rated 1,600 rpm torque peak, so that number is not something you actually use in normal operation. What matters is torque rise—the increase in torque as the engine pulls down toward the backshift point. On our chassis dyno, this truck averaged about 420 rear-wheel horsepower at 2,800 rpm, then climbed from 788 lb-ft at horsepower peak to 898 lb-ft at the backshift point around 2,150 rpm. That 110 lb-ft gain, or 14% torque rise, is the truck’s real lugging ability. We also test with the hood down and road-speed airflow into the nose, because underhood heat and bad dyno setup can skew the result fast.
The video centers on a new GMC Sierra Denali Ultimate 3500 HD equipped with the 2024 Duramax L5P diesel. GMC rates the truck at 470 horsepower and 975 lb-ft of torque at the flywheel, and the purpose of the test is to determine how much of that output actually reaches the ground through the complete drivetrain. At the time of filming, the host notes that only two examples were in California, underscoring how new the truck was when tested.
Before moving to the dyno, the recap walks through the truck's premium equipment. Up front, the Sierra uses redesigned LED headlamps. The truck is fitted with 14 cameras, including the system that allows the driver to effectively see through a trailer. It also has retractable side steps with integrated LED lighting.
Inside, the truck is positioned as GMC's top-tier luxury heavy-duty pickup. It includes a 12-speaker Bose audio system, wood trim identified as Paldao wood, and machined artwork on the glovebox door. The cabin also features a 12.5-inch driver information center and a 13.4-inch infotainment screen. Around the back, the truck carries GMC's MultiPro tailgate, and the front seats are 16-way power units with a massage function.
The host briefly summarizes the engineering updates made to the 2024 Duramax L5P compared with the 2023 version, referencing a prior teardown video. According to that comparison, the 2024 engine receives a new turbocharger and vane actuator, new pistons with tapered bowls intended to improve combustion, and revised cylinder heads with improved water jackets. The fuel system is upgraded with higher-pressure injectors and new fuel rails designed to withstand the increased pressure.
Additional changes include improved glow plugs, stronger valve springs that enhance engine braking performance, and a completely new engine control module. That ECM uses GM's Global B electrical architecture and hardened encryption. These updates form the technical basis for the truck's higher advertised output.
To measure real delivered power, the truck is tested on a chassis dyno rather than relying on flywheel estimates. The Banks facility uses a large front-mounted wind machine that the host describes as a long-developed in-house setup. It supplies roughly 40,000 CFM, producing about 60 mph of airflow directly into the nose of the truck. The goal is to reproduce road-speed cooling and underhood thermal conditions as closely as possible.
The test is intentionally performed with the hood closed. The host emphasizes that testing with the hood open and a simple shop fan in front of the vehicle does not replicate real driving conditions. Underhood heat load must match what the truck sees on the road, because intake air temperature has a direct effect on power. He points out that on an 80-degree ambient day, underhood air can reach 180 degrees, which is especially relevant for aftermarket intake systems that draw hot air from the engine compartment through an open-element filter or a loosely shielded enclosure.
The chassis dyno is presented as a way to remove environmental variables that complicate road testing. Headwinds, tailwinds, traffic, and changing weather are eliminated, allowing the team to sweep the engine in controlled increments, approximately every 50 rpm, in a manner closer to engine-dyno methodology. The difference is that this setup measures the complete powertrain, including drivetrain losses, and reports what actually reaches the rollers and therefore the road surface.
Several supporting measures are used to keep the test stable and repeatable. A large bag of sand is placed in the bed to help prevent the truck from becoming unstable or spinning the tires on the rollers. Additional cooling is provided by wall-mounted blowers feeding 8-inch tubes routed under the slab and into the dyno pit. These cool the rollers, the tires, and the dyno absorber units located under the yellow covers.
The test procedure begins near the engine's horsepower peak, around 2,800 rpm. From there, the dyno loads the truck and pulls engine speed downward to observe how torque builds as the engine lugs. This is important because the host argues that the published torque peak of 975 lb-ft at 1,600 rpm is not something the driver can normally access in real operation.
In this truck's 10-speed automatic, a wide-open-throttle pull causes the transmission to backshift at about 2,150 rpm before the engine can be dragged down to 1,600 rpm. As a result, the meaningful torque figure is not the brochure peak at 1,600 rpm, but the torque available at the backshift point. That is the torque the driver can actually use before the transmission intervenes. The host frames this as a more realistic measure of usable performance, especially when towing or climbing grades.
The team performs three runs and averages the results. The truck tested was essentially stock and very fresh, with about 1,600 miles on it. At approximately 2,800 rpm, which corresponded to about 78 mph on the dyno and aligned with the horsepower peak, the truck produced 420 rear-wheel horsepower and 788 lb-ft of torque at the rollers.
As the dyno pulled engine speed down and the transmission finally backshifted at roughly 2,150 rpm, rear-wheel horsepower at that point was 368 and torque was 898 lb-ft, effectively almost 900 lb-ft at the ground. The host reminds viewers that GMC's advertised 470 horsepower and 975 lb-ft are flywheel numbers measured before the transmission, torque converter, driveshaft, transfer case, and other drivetrain components consume part of the output. The dyno figures therefore represent delivered power after those losses.
The key conclusion is not just the peak rear-wheel numbers, but the torque rise between the horsepower peak and the backshift point. Torque increased from 788 lb-ft at 2,800 rpm to 898 lb-ft at about 2,150 rpm. That is a gain of 110 lb-ft, or roughly 14 percent. The host identifies this as the truck's torque rise, a concept commonly discussed in heavy-duty commercial diesel engines because it reflects lugging ability under load.
In that context, torque rise describes how much additional pulling force the engine develops as rpm falls before a downshift becomes necessary. The host argues that pickup buyers should pay more attention to this characteristic, because it better reflects towing behavior than a brochure torque peak that the transmission will not allow the engine to reach in most gears. By that standard, a 14 percent torque rise is described as very respectable.
The overall impression is that the 2024 truck is clearly stronger than the 2023 version. Even though the full advertised 975 lb-ft at 1,600 rpm cannot be directly experienced in this test because the transmission backshifts first, the measured rear-wheel results and the 14 percent torque rise show a meaningful improvement in usable performance.