In any job, there are bound to be some days that are just better or more exciting than others. For instance, I feel certain GMC’s research and development department enjoyed the days it spent testing a new carbon fiber Sierra bed by throwing cinder blocks at it, dropping 450-pound steel drums in it and revving a snowmobile with medal studs on its track to full throttle while the snowmobile sat in the GMC’s bed. GMC touts its carbon-fiber composite bed as less corrosive, more scratch, dent and corrosion resistant, and it cuts around 60 pounds of weight over a traditional steel bed. And there is no need for a bedliner.   Buyers can opt for the carbon fiber bed as a part of the CarbonPro package available on the Sierra or off-road tuned Sierra AT4. It is a pricey add on at $8,965, but there are plenty of other desirable features in the package. It also includes an upgraded sound system, HD surround vision, a clever rearview mirror that displays the image captured from the rear camera, 22-inch black wheels, power sunroof and power retractable running boards. Also included are safety features in the form of forward collision alert and lane keep assist, along with adaptive cruise cont...