I have to give it to them they did one hell of a job with it.
http://www.callawaycars.com/callaway...ckMainPage.htm

Based on the current Chevy Silverado 1500 half-ton, Callaway is amping up both the 5.3-liter V-8 and 6.2-liter V-8 haulers with Eaton's Twin Vortices Series roots-type superchargers. The same superchargers are used to boost power to stratospheric levels in the Chevrolet ZR-1 and Cadillac CTS-V.

Callaway's powertrain tweaks also feature an air-to-liquid intercooler system plus high-capacity fuel injectors and a high-flow air intake system.
The bottom line is 450 horsepower high up the curve (at 6,200 rpm) and 450 pounds-feet of torque (at 4,000 rpm) in the 5.3 and 540 horses (at 6,200 rpm) and 522 pounds-feet (at 3,800 rpm) in the 6.2, according to Callaway's website. That's an increase of 135 hp and 115 pounds-feet of torque over the stock 5.3 and 137 hp and 105 pounds-feet over the stock 6.2.

Despite the huge performance gains, Callaway promises the trucks will keep the same fuel economy ratings as the standard Silverado, which the EPA rates at 15/21 mpg city/highway for the 5.3 4x2 and 13/18 mpg for the 6.2 4x2.