I'm logging, and feeling, spark reduction of 17-18* and up to 2 sec duration that appears to be associated with A/C clutch engagement/disengagement. I have logged all spark PIDs and the only one that is active at these times is Total Torque Control Spark Retard (GM.EST_TRQ_DMA). None of the PIDs that are supposed to contribute to this PID are active(trans torque reduction, traction control, brake torque). There is no activity on the A/C Compensation Spark PID.
Does this make sense?