What controls timing on a '99

I'm still chasing my hesitation problem. While cruising at 3-4k the power slightly dips in a rhythm. The way the power cyclically hesitates while cruising makes me think it is either a sensor telling the ecu to pull timing or it's the mechanism that controls the timing itself. Thoughts? The cam angle sensor is only 4-5 yrs old. I plan on looking into the throttle position sensor as well.

Full throttle pulls seem ok, at least okish. This makes me think it's an open loop issue. I guess the O2 sensor could be faulty?