So I've spent hours and hours doing research on here before having to ask the questions (rare, I know
My '11 LTZ with 125k recently started doing RPM drops.
They are pretty often, whether I'm in or out of cruise control. It occurs at city or highway speeds...even on my 25 mph residential street. It's more noticeable uphill (speed stays steady).
Sometimes it's just a quick drop, other times it feels like I'm going over a rumble strip.
I performed the obvious maintenance after reading the forums: Transmission fluid drain and fill, purge valve replaced, coil packs all tested ok and new spark plugs were installed.
After the new plugs it seemed to drive normally for the first 5 miles, then the RPM drops slowly came back to their recent level after another 10 miles.
I've also noticed a drop in MPG if that helps. I was at 19.5 avg, now down to 18.
The RPM fluctuation is usually around the 200-300 range.