Annnddd......I spoke too soon. Just a few hours after posting my message saying it was fixed, I have now experienced the same issue. Major problem is we just took this vehicle on our vacation and are now 10 hrs from home. I was able to get it to go into gear in order to get it back to our rental property but it was too late in the evening to get it to a GMC dealership. I'll be taking it first thing in the AM, assuming the car will shift into gear, so I'll update once I know more. I also have recognized a new symptom to the problem. If I try remote start and it doesn't work (lights flash but engine does not start) that is an indication that when I crank it, it will not be in gear (doesn't show P illuminated) and it will not accept a gear change. Today I simply turned it on and off multiple times and eventually after about 15 minutes of this, it finally worked. Beyond frustrated at this point.