Went from 93 to 92 octane and started getting KR??
Maybe some bad gas?
Check the back side of the TB blade and see if it's very oily in the intake tract. During extended cruising mine seems to suck more oil through the PCV. If so, try cleaning out the TB/Intake with some throttle body cleaner. It's been my experience that an excess of oil coming through the PCV /intake seems to cause KR.
At around 45,000 miles I had to use the GM top end cleaner on mine to get rid of KR.


