Stock is good, but there's always room for improvement. When GM Powertrain set out to build a Duramax-powered GMC truck to help promote its new Duramax boat engine, it turned to Diesel Power to develop a concept. Knowing that it would need a truck that could tow and be reliable, we hooked GM Powertrain up with the folks at Gale Banks Engineering for the installation of an exhaust system, intake, high-performance intercooler, and one of Banks' new LMM Six-Gun programmers with the PDA option.
A balanced approach is what we were aiming for, as the intake and exhaust upgrades would allow for cooler EGTs and more airflow than the stock pieces. With the Six-Gun rated at 110 horsepower, and a 165 lb-ft increase over stock, plenty of air would be a great help. It should also be noted that no emissions equipment was compromised during this install, and all the parts and pieces work with the LMM's diesel particulate filter.
During our test drive, the truck was slowly increased from level one to level six on the PDA so the Allison transmission could try to "learn" the appropriate shifting pattern for the power increase. Once at level six, it was a completely different truck, spinning the tires at will and sprinting up to speed. The intercooler and exhaust also allowed the truck to make 38 psi of boost at its peak, which is the most we've ever seen on an LMM. Exhaust gas temperatures were completely under control at 1,400 degrees, and the truck didn't throw any codes or check engine lights. The Banks tune is also a "clean" tune, which means the DPF should live a long and happy life. Now this wild camouflaged truck not only has the looks, but the performance to match.
Since it would be the most time consuming, the intercooler installation was first. We started by removing the grille of the truck. | 
The headlights were next. They're plastic, so we were careful not to break them when prying them out. | 
We had a few other accessories on the truck to deal with, such as cameras and off-road lights, so we marked all the connections to make sure there would be no confusion during reassembly. |