OMG!!! I just went through the exact same thing starting 3 weeks ago. Dealership eventually replaced all right side lifters and injectors, VLOM, 1 pushrod (not all 8), various gaskets, oil, etc. Dealership had it 2 weeks. During the first test drive after initially replacing 2 injectors and a lifter the pushrod broke. My symptoms were exactly the same except that I hadn't heard the ticking noise for very long at all.
2016, Denali, 6.2 with 56,1xx miles... and thank goodness for the extended warranty.