Check Engine Light On problems of the 2011 GMC Canyon

I am experiencing problems with this vehicle that are terrifying as it is putting my family in jeopardy. My first indication of a problem occurred in August 2013 and continued until may, 2014, the problem seemed to have fixed itself as I did not experience any more serious problems after may 2014 until October 2014. This leads me to believe the problem seems to have some connection to colder weather. The stalling problem is now occurring regularly and the error messages tend to disappear overnight before I can get to a dealer. I am keeping my driving to a bare minimum until a satisfactory solution is found. I do not want to spend more money on parts and “fixes” that do not resolve the problem. Problem: car suddenly reduces speed with numerous error messages running across the dash screen. I fortunately have been able to pull over to the side of the road as speed was very slow; the car begins to shudder and I have to shut down the engine. I noted the following error messages: reduced power, trac fault, ser stab, sist traction. After a few minutes I have been able to re-start the engine. When restarted all the error messages disappeared, but the check engine light stayed on. Various error messages: p0657 (dealer installed peddle position sensor 1/23/14 @ $229. 63); same problem occurred 2/19/14. P0615 (dealer installed throttle position sensor @ $100); same problem again occurred 3/13/14. I cannot afford to keep replacing “out of warranty” parts that do not correct this serious problem. Reduced power has occurred a number of times but the error messages disappear before I can get to a dealer. Since the dealers were not able to pin point the problem, I appealed to gm to advise how to proceed to resolve this serious problem before it results in a serious or fatal accident.