To follow up with my tail light post. I had finished doing the exhaust flapper mod, and when I started the Yukon to back it out of the garage, I noticed the passenger tail light was out. I hit it a few times with my hand and it would intermittently work. The LED tail lights are a sealed unit and a replacement is $500+..
After an online search, it appears this is an issue with all 2015+ Yukon models. What is happening is the thin metal that connects each LED on the sealed inside of the light is cracking. I pulled my passenger tail light off, melted the plastic with a soldering iron around each area that is known for the cracking issues and found the bottom side was completely cracked and the upper side was starting to form a crack. Even though the driver side was still working, I did the same and sure enough, cracks had formed on that as well. It wasn't if, but when it would fail.
Some people were soldering a piece of wire as a jumper to each side. I found it easier and cleaner to just run a bead of solder up the original piece without adding a piece of wire. I completely spaced taking before photos, so the first photo I borrowed from online, showing the exact same crack I had. The rest of the photos are mine, show the solder repair, as well as closing them up. I just used Gorilla Tape and silicon on the seams of the tape. They work great now!