Cruise control going up and down?
 

For some reason the cruise control on my 2011 SL550 (no distronic) is acting weird, if I set the cruise to say 75, it'll drop down to 70, then rev up to 75, then drop back down to 70 and keep going back and forth, anyone know what's wrong or could point me to which module to look at? I have a Launch scanner that can read OEM codes and modules.

could your tyre sizes be causing this? if the outer circumference is different from front to back it can cause issues.