I'm making some more adjustments for this, but like I said previously... without logging all the airflow pids it can be difficult to get a really nice return to idle.
The PCM does a whole bunch of diagnostic tests while you're driving... this is one of those tests. It will only ever do it at idle. I'm guessing that GM figured that sending you lean at idle was the safest time to do it. Unfortunately, we have no way of disabling this test. It's something you just have to live with.
Yeah, your last log doesn't look all that bad. We'll still do some more changes and see if we can clean it up a bit more.