The real key is what the #'s look like when GM reports Q4 #'s in January, 2020 since they'll have been in full production of the new HD's in Q3 and they'll have a completely redesigned product competing with a 4.5 RAM HD. If RAM continues to outsell them at that point, then you're going to have a lot of concern in the GM board room.
Personally, I wanted to purchase the new Sierra HD Denali, because for my application, the tailgate is a much better fit for my needs. But, ultimately, when I saw their interior at the San Diego launch of the HD's and heard their marketing speak of going for durability vs. luxury, it convinced me to not wait for the fall rollout.
Even with the old 4th Generation cab, RAM has moved the interior forward. If GM wants to claim their Denali is luxury, they're going to have to upgrade the interior as well, or they're going to lose pricing power. So, the question is does GM want to bite the bullet and take the margin hit now, or later. My money is later based on prior behavior. By that time, GM will most likely be in a distant third place in the truck wars.