weird dips in timeing under cruise rpm

[Black'Rado]

i just recently bought this 03 silverado ss with the lq9. it has headers, cold air, and a 2400-2600 stall the best i can tell.
i started to feel the rpms surge some while cruising so i set up this log and it looks as if the timing just takes random dips down and then back up? the truck does have a tune on it from a popular company but its just a mail order and was from the previous owner. also seemed to pick up quit about of KR from a 60mph roll.
Im just curious at what is causing this.
17385

[JUSTASBC]

I had an issue like this but it would only do it when the blower motor was on. Try turning it completely off and see if the problem continues.

[darcy]

You can log all of the EST pids to determine what it is that is affecting spark.

WRT knock - 30deg is way more timing that it needs/wants at such a load point.