We were traveling not once, but twice at a high rate of speed (75/80mph the legal limit) the vehicle gave one message: Service power steering next message: reduced acceleration. The check engine light turned on, the truck itself jerked and we almost lost control of the vehicle (both times) on the highway. We were thankfully able to pull over and pull to a complete stop. The vehicle was still on, it still ran but I saw an autozone close by both times and received a code for the check engine light. The dashboard both times lit up like a Christmas tree on both occasions before spazzing out. We have taken the truck twice to a nearby dealership and they were able to service and fix the problem however they said that the first time, and here we are a second time. The dealerships we took the truck to are aware of all the codes (2 pages worth the first time) but we never received paperwork on what was fixed. The second time we are now going to pick up and hopefully receive paperwork on what was completed. My spouse was driving and myself and my daughter were in the vehicle when the jerking happened with the steering wheel. The vehicle is not safe how can I we be driving at the legal limit and lose control of our vehicle. We were right next to an 18 wheeler with a trailer and multiple vehicles on the road each time. The GMC dealerships are aware they have been working to fix the problem however again this is the second time it happened. The messages occurred both times. Service power steering and reduced acceleration check engine light and also no traction control. The first time it happened was [XXX] going to Killeen Texas and the second was [XXX] going to Albuquerque. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)