I have the same issue. I am extremely particular about my vehicles and I'm not happy about this. I had this truck undercoated when brand new 18 months ago, and the frame is rusting badly where the tubular cross sections are welded to the boxed frame, both ahead of, and behind, the rear axle. It has 17,000 miles on it now. My son has a 2014 Silverado with the same mileage and exactly the same amount of rust in the exact same spots, and his was never undercoated. I went to the undercoating shop today and talked with them, and they told me this: GM, unlike Ford, beginning around 2012 sprays their frames with a sticky protectant so when they arrive at the dealers, the frames look good. When the undercoating is sprayed on a new truck like mine, it sticks to this protective coating, but this coating isn't a long-lasing protectant, so when it separates from the frame, the undercoating comes off with it... then the frame rusts. Therefore, both my son's truck and mine look equally bad even though mine was undercoated and his wasn't.
Of course, this could just be a line they're telling me to absolve them from any warranty or liability, but it actually made sense to me if it's true. I have had numerous other Ford trucks and GMC (pre-2012) undercoated when new and never had this happen until this 2014 GMC. I am going to take pics of both mine and my son's trucks and take them to the dealer and ask about the TSB mentioned elsewhere in this thread. I'll repost with any news.
Thanks guys.
