I had a similar issue recently. I recently had the engine replaced in my 2011 Denali. After a few hundred miles, I was filling up at a gas station (car running) and I got the same error message as you did, and the A/C shut off. On the drive home, I paid close attention to the temp gauge and saw it see-sawing left and right like a slow metronome. The cool air flowing through the radiator brought the temps down though and the A/C returned. When I got home, I cracked open the (half full) overflow reservoir and all the coolant sucked up into the engine! I suspected they did not properly burp the coolant system after installing the new engine. I added coolant, started the car and continued to burp the system. It took another half gallon of coolant. I kept an eye on the temps whenever I drove it for the next two months and noticed some minor movements and some leakage on the ground. I feared a blown head gasket but I was getting a vacuum in the reservoir, not bubbles, white exhaust smoke or odor. Sometimes I had to add a little coolant during the week and then the next day it blew it onto the ground. I remained perplexed for a month of troubleshooting until I found coolant on the water pump (another minor panic). I determined it was coming from the top radiator hose. They did not tighten the clamp enough on the hose at the water pump and the hose was very loose in my bare hand. In my opinion, the I.D. diameter of the hose and the O.D. of inlet do not mate up closely enough, on top of the clamp tension. I tightened the bejesus out of the worm-drive clamp, added a little coolant and continued to monitor. After a month of observing - the puddles under the car are gone and the temp has stabilized in the center of the gauge. The loose hose would also explain the air entrapped in the system as the pump was sucking air into the system.
