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2003 GMC Sierra 2500HD: 600hp Work Truck

Runs 12s and Still Makes a Living

Mike McGlothlin
Jan 1, 2011
Photographers: Mike McGlothlin
Sometimes it's the things that aren't done to a vehicle that make it impressive. Take Caleb Carpenter's '03 GMC Sierra 2500HD for example. With a factory fuel system, no lift pump, stock injectors, and a factory CP3 from an LBZ engine, this standard-cab Duramax still cranks out nearly 600 hp at the wheels. And the best part? Making power isn't even his top priority with the truck-making a living is.
Photo 2/12   |   1101dp 2003 Gmc Sierra 2500hd 600hp Work Truck front Three Quarter Shot
Caleb, a hay farmer with fields throughout west-central Indiana, purchased his Sierra with just 36,000 miles on the odometer and immediately put it to work. It pulls a 32-foot gooseneck trailer-often weighing in excess of 20,000 pounds when loaded-on a regular basis. The 3/4-ton also gets a reported 13 to 15 mpg while towing, and more than 20 mpg when empty.
Most diesel pickups are used for day-in and day-out work schedules, but Caleb found time to make the truck more enjoyable on his days off. Within 30 days of buying it, Caleb had the Duramax breathing easier, thanks to a 4-inch exhaust and an AFE air intake, and he got it running strong courtesy of some EFILive fine-tuning by Fleece Performance Engineering.
Photo 3/12   |   The truck only had 36,000 miles on it when Caleb picked it up, and the LB7 under the hood has been solid and reliable. Like a lot of other LB7 owners, Caleb has had to replace the factory injectors, but with 119,000 miles now on the clock, the engine basically has a fresh start. The truck laid down 585 hp and 1,128 lb-ft on Danville Performance's dyno-a solid number considering he's not running a lift pump. This winter, Caleb plans to add an AirDog fuel system to the truck, which will allow him to squeak 600 hp out of his current combination.
Several months later, and with 50,000 miles on the clock, the stock five-speed Allison transmission was pulled and upgraded to a Stage III unit from Sun Coast Converters. Sun Coast's triple-disc 1058 torque converter was also added, which is ideal for trucks running big-horsepower tunes. After that, a custom, wastegated S300 turbocharger with a 2.5-inch inducer from Fleece Performance replaced the factory IHI unit. For fuel, a Fleece Performance modified CP3 injection pump from an LBZ engine replaced the factory CP3 (the LBZ pump flows roughly 10 percent more fuel).
Once the power-adders and the tough-as-nails transmission were bolted in, the truck was tuned once more to get the most out of its current setup. A DSP5 switch allows Caleb to change the engine's tune on the fly, and a Fleece Performance TapShifter gives him complete control over the Allison's gear selection. Most recently, the truck's factory LB7 injectors, which were causing excess smoke at the tailpipe and poor mileage, were replaced with a set of brand-new OE units for a fresh start.
Because the truck spends a lot of its day slowly moving through fields with a load in tow, Caleb knew something had to be done to keep the Duramax cool on hot summer days. So he installed an electric, dual-engine fan from Flex-a-lite, which not only keeps the LB7 running cool, but also provides quicker engine warm-up and cooler A/C output.
In case you're wondering, the red paint Caleb's truck wears isn't original. To make a long story short, a drunk driver actually forced his Duramax (and the trailer behind it) nose first into a ditch, resulting in a white-knuckle ride and considerable damage to the passenger-side door. When it came time to repaint the truck, which was originally GM Victory Red, Caleb wanted something a little different. "I was never a big fan of the original red paint, so I told a friend to come up with a unique color," he told us. "I still wanted red, but something with some metallic in it-and he pretty much nailed it for me." In fact, it's very similar to Dodge's Inferno Red clearcoat, although it's from PPG and has just enough metallic in it to appear orange in the right lighting.
A standard-cab Duramax with an 8-foot bed is pretty unique in a world now chock-full of four-door shortbed trucks, so we give Caleb props for being different. It's also nice to see a truck earn its keep day after day towing 20,000 pounds and still be capable of running a 12-second quarter-mile or hooking to the sled with the flip of a switch. If we were in the market for a Duramax, we would want something like this: lightweight, four-wheel drive, and plenty of power to handle any job.

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