2013 GMC SIERRA 2500 Engine Problems

I have a 2013 GMC Sierra, purchased new in 2012, has approximately 35,000 miles. The check engine light came on while driving and suddenly another light came on. Then a third light came on claiming poor engine fluid quality. I immediately stopped at an auto parts store and put DEF fluid in the pickup and continued to drive thinking the lights would go out, but instead a warning was flashing on the dash that says after so many miles the truck will be slowed down. We started getting nervous because we were driving on the highway and if the truck suddenly slows down whilst driving in highspeed traffic, our slower vehicle would potentially cause a collision and put us and others in harms way. In reading your own safety site, there is a recall on the vehicle regarding faulty airbags, so it could be even worse! In our investigations of...