Have 2012 Z71 4x4 crewcab. 5.3ltr 3.42 locking rear active fuel management. 30 k miles. Must say the first 10 k did take some time to get use to shift patterns. The throttle is your friend. Give the truck some gas and she will go. My average economy is 16.8 over the 30 k so not great but acceptable. I have a service advisor who is a friend that told me to drive the truck like a truck and not worry with the mileage and the shifting issue would settle. That part did. The mildly rough idle well that is still there. No rear end clunk

 

I have found that I can "force" the rear end clunk by how hard or quickly I stop... smooth slow stops, with minimal braking, or slowing enough to be able to let up off the brake peddle just as I stop produces no clunk at all...

Hard stops seem to load the rear end and once the transmission downshifts after the complete stop is when you get the clunk....