Today I was driving my truck, a 2006 GMC Sierra 2500HD with Duramax Diesel and Quadzilla programmer, and decided to pass a car uphill(probably a little faster than I should have). As soon as I passed it, the check engine light came on. When I got to the next hill, I seemed like it didn't want to accelerate despite giving it gas(slipping tranny?). I immediately pulled off to the side and turned it off and back on. It started doing it again, not accelerating after about 50. So I put it into the manumatic gears for a little while. I then put it back in drive and it worked perfectly and is still working perfectly. The check engine light also turned off. This has never happened before. What seemed to be the problem and should I be worried?