Unfortunately, for all of the engineers that worked so hard getting the Allison to work seamlessly and be more efficient, the Duramax stole the show. It's been on the scene for 10 years now, and it's no stranger to the diesel community. The aftermarket welcomed it with open arms, as did a large number of drag racers, sled pullers, and everyday, average trailer users. The LML is definitely worthy of carrying the torch for the current HD trucks, it's nothing short of a beast. Merging uphill onto highways was not a problem, even with a big load behind us, as the Duramax pulled steadily no matter the engine speed. The fact that Duramax engineers were able to coax an additional 30 hp and 100 lb-ft out of the same engine platform is impressive, but the fact that the new engine is quieter, cleaner, more fuel efficient, and under no more stress than previous versions is proof that this wasn't just a simple engine software upgrade. With new injectors, pistons, bearings, and oiling characteristics, the LML Duramax offers several small, but significant, upgrades over the previous generation. The only new factor that owners will have to deal with is the Diesel Exhaust Fluid (DEF) system that reduces the Duramax's NoX emissions by over 60 percent. A 5.3-gallon tank under the passenger-side footwell is accessed through a filler neck under the hood, which is appropriate since the fluid will only need to be topped off every 5,000 miles (about every oil change). Further improvements in the emissions system include a diesel particulate filter system with an extended regeneration cycle. The system can go as far as 700 miles before the downstream injector supplies extra fuel to clean the filter. The extended regeneration cycles cut fuel usage, and the use of a downstream injector keeps additional unburned fuel from seeping past the rings and contaminating the oil.
Another improvement that was soon appreciated was in the steering. We didn't have a 2010 Chevy HD on hand for a direct comparison, but a quicker steering ratio and larger steering gear eliminated any play and felt nicely dialed in. The steering response, engine power, engine braking, and exhaust brake all translated to immediate driver confidence. The truck never got out of balance or felt like it had a mind of its own. In fact, we set the cruise control and let the truck handle the speed going up as well as going down the 8 percent grades, making for a relaxing drive even though we had over 35 feet of trailer hanging off the back.
After a suggestion from a colleague, we drove identical loops back-to-back, first with 2,000 pounds in the bed of a single-rear-wheel Chevrolet 3500 4x4 with the brand-new Duramax and then again with 2,000 pounds in the bed of a single-rear-wheel Ford F-350 4x4 with Ford's brand-new Power Stroke. Both trucks are remarkably powerful. Chevrolet and GMC have the bragging rights for now with a 7 hp and 30 lb-ft advantage over Ford, with 397 hp and 765lb-ft of torque, so both have enough power to haul just about any tool or toy you'd care to load on a trailer, and it's practically too close to call from the seat of the pants feel. What's easier to perceive is engine noise and ride quality. Cruising on an even stretch of highway with the engine at around 1,700 rpm you'll struggle to hear the Duramax, while the Power Stroke has a noticeable rumble as well as turbo whine. We didn't really mind the engine noise from the Ford on our short time behind the wheel, but it's one of the factors that GM engineers addressed in their HDs to reduce driver fatigue. The fewer distractions and annoyances, the better. As for ride and handling, the IFS certainly has its advantages compared to the solid axle front suspension in the Ford and Ram. IFS allows for a better contact patch for steering and braking, and obviously each side can react to bumps on its own. On the relatively new asphalt highways we were on the difference was subtle, but noticeable. Where the Ford and Dodge solid axles prevail is in the sort of off-road environments where extreme wheel travel and low speeds are the way to go, but on the highway there's no question that IFS rules. Before we get hate mail from Ram HD or Super Duty owners, we're not trashing the ride of your trucks, we put thousands of miles in a Ram HD earlier this year and didn't have a complaint,-it's just that these trucks are even better in that regard.