Cruise Control "shudder" & not constant
 

I took my 2015 Z51 (A8) in for the airbag recall and oil change this past week. On the way home at about 65 mph in cruise control I noticed a “shudder” or "rumble". I use cruise control a lot and I never experienced that before (11k miles). It almost is like hitting a rough spot in the road or going over a rumble strip on the edge of the highway, only more subtle. The speed control doesn't hold the speed constant and I noticed that the RPMs were undulating in sync with the "shudder" and speed. The RPMs increase by 1 or 2 hundred and then fall back. It's during the decrease in RPM that the "shudder" occurs. It is true that there is a slight roughness when going from 4 to 8 cylinders but that is only momentaryand when RPMs are going up.
Time to go back to the dealer I guess. ?? I can't be the only one with the problem.

Did you ever get an answer to your problem, I have the same issue. When in manual I do not have this shutter only when in automatic and the RPM's drop 100-150 then surge back up.