Power Steering Failed problems of the 2013 GMC Sierra

I own a 2013 GMC Sierrahd 2500 and I am expieriencing power steering failures. GMC is refusing to fix the problem because they cant find it. GMC also has no problem putting me back on the road in a dangerous unsafe vehicle that is still under bumper to bumper warranty. . The first expierience was just pulling into a parking spot. As I was turning, always to the left, into the spot the power steering failed. Always after a long drive this occurs, to the tune of 5 plus hours. The power loss repeated itself two more times that first day. Occuring when I was coming to a slow left turn under 10 mph. I took it to the dealer a couple days later and they couldnt repeat the problem so they refused repairs. The next time it happened was a couple days ago. This time it began with slow left turns in a parking lot or on downramps from highways. However the problem gained intensity as I thought I could feel it while driving at high speeds, although I direguarded that since it is hard to tell while driving 65 on the highway. Once I reached my local back, curvy, mountain roads, it failed repeatedly. One instance causing me to veer to the edge of a severe drop off and my tires running off the road. This easily could have been a fatal moment. Again after a long drive, they were unable to recreate the problem. They inspected everything and researched the issue. GMC said that will happen when hitting the brakes at a slow speed. However, the failure has now occured without braking and at a normal speed of about 30 mph. GMC refused to replace anything and would not compensate the dealer if they did. Thus GMC put me back on the road in a dangerous vehicle. They said this was normal and would happen from time to time. Despite all their excuses, I had a contradiction for. I dont understand why it didnt start till now and why am I the only one having the problem.