14sierra-gmc

I have a 2014 GMC Sierra that I purchased new in July 2014. The only issue that I've had was with the driver's seat clip. However, about a month ago I started having occasional problems with it not starting. About one month ago, I tried to start the vehicle and the engine didn't crank. I tried again, and it started fine. However, the display said something about service theft deterrent system. About two weeks later the same thing occurred. Today was the scary part though! I was in the drive through lane at a restaurant. I just received my food. The vehicle was in drive and I accelerated to about 2-3 MPH. Then it died. I immediately put it in park and tried to start it again. It didn't start. I tried again, and it started fine, but again said service theft deterrent system. I drove it on home without any more issues. It scared both me and my wife, since it was actually in drive and just died without warning. I would have hated to been driving at full speed. I'm taking it to the dealer at 8:00 AM Monday morning to let them figure it out. Does anyone have any idea as to what could be causing this issue or has anyone else experienced it? Thanks, -w