Quick update...
So they did find the issue right before our trip. Turned out it was a wiring issue from the PCM to the solenoid. Apparently the factory support group reached back out to the dealer with a "try replacing this wire". They did that and it fixed the limp mode issue. We towed from PA to FL and back without any truck running issues. Now the check engine light did come back on on our way home so the truck is back in the shop, but it was nothing obvious. Seemed to run fine so hopefully a small warranty issue.
To those saying ditch the truck, I really don't want to. I really like the truck and with it having 4:10 rear it tows far better than I had expected a gasser to tow. I have owned diesels in the past and even during a 1000 mile tow I do not find myself wishing for another truck. I really have no complaints until I started with this whole limp mode issue and now this engine light issue, so I hope they get it figured out and I am good to go. Even if I wanted to trade it I still owe a lot on it, the dealer has 3 or 4 heavy duty trucks on the lot right now, and what they do have offers minimal discounts. My local GMC dealer has 1 Heavy duty and the Ford dealer has 2. All 3 dealers typically have an entire lot filled with dozens.
Anyway, thanks for all the help, just figured I'd share that it turned out to be a wiring issue.