More than 11,572,000 '99-'06 GM pickup trucks (known as GMT-800s) were built, and the last one rolled off the assembly lines in February. Don't worry, the General now has a new GMT-900 for Chevy and GMC lovers. It comes with the Duramax LMM clean-diesel engine making a best-in-class 365 hp at 3,200 rpm and 660 lb-ft of torque at 1,600 rpm; a six-speed Allison transmission with manual shift mode; a new steering-control system; and a brand-new, stiffer body and interior. That's all attached to a stronger frame with the familiar independent front suspension with torsion bars and an 11 1/2-inch AAM axle on leaf springs in the rear. We recently got our first chance to drive the 3/4- and 1-ton trucks in all of their cab and bed configurations. We think the GM crowd will be quite happy with the new addition to its family.
The new Duramax LMM engine...
The new Duramax LMM engine makes 365 hp and 660 lb-ft of torque while meeting strict '07 emissions regulations that cut soot by 90 percent and nitrogen oxides by 50 percent.
To meet strict '07 emissions regulations, the Duramax LBZ had to be saddled with a larger exhaust gas recirculation (EGR) system, an oxidation catalyst, and a big diesel particulate filter (DPF). It also gained new seven-hole injectors, a boreless turbo, and an electronic intake throttle. Incredibly, the engineers were able to meet emissions while making more power than the Dodge Cummins and Ford Power Stroke engines-and you can feel it.
The trucks accelerate with ease, and from a dead stop, you can break the tires loose in a Crew Cab dualie for at least 10 feet. The electronic throttle does not have the detached, drive-by-wire feel we've experienced in other trucks caused by computer intervention. Instead, this clean Duramax seems to be programmed to obey orders instead of debating them internally before fueling the engine. Of course, the computer is working very fast but seems to stay in the background-and it's more than welcome to stay there. Even when the emissions system goes into regeneration mode, which alters engine functions to burn off soot, the LMM is designed to only raise the idle by 100 rpm and remain undetected by the driver.
The new boreless turbo uses...
The new boreless turbo uses a one-piece exhaust turbine that's stronger because the shaft does not pass all the way through the center of the wheel. This design allows faster turbo speeds because the base of the fan blades is more rigid.
Driving these trucks while they're unloaded is downright sporty. The variable-geometry turbo is always ready to spool, and torque builds quickly. The steering has a great on-center feel and is very predictable, especially when compared with trucks with a solid front axle. This, combined with big disc brakes at each corner, makes it tempting to take turns at illegal speeds. Some of the trucks we drove included a payload in the bed, but if it weren't for the "P" sticker on the windshield, it would've been easy to forget the trucks were laden with more than a ton of weight. The torque available throughout the rpm band easily masks the added weight until you feel the extra inertia you're carrying into a turn or stop.