I wanted to update this as I encountered something today that seems like it could play a role in the fuel trims...but time will tell.
Maybe this thread jinxed me..lol, but a few days ago I was seeing high negative LTFT's, a bit higher than what seemed to be regular.
I was getting around -11 to -13ish % LTFT at idle, driving was fine..around -2 to -7. So I wanted to see what happens when I disconnect my MAP sensor so I pulled the connector with the engine idling and the motor stalled. I reconnected the sensor and restarted the engine and it immediately had a misfire on one of the cylinders.
I checked the torque app and it was Cyl #1, I lost the coil. I replaced the coil and now my LTFT's at idle are back down to -7 to -8 with the A/C on.
As of yesterday, my LTFT at idle with AC off was -13, with A/C on was -10. Not with the coil replaced I have -10 with A/C off and -7 to -8 with A/C on.
Could be the coil was on it's last leg as it is the original, I've only replaced the #4 and #2 coil since I bought the Envoy new.
Maybe it was nothing, but maybe the remaining coils are weak and while not causing a misfire, but not a complete combustion..
I'll give it a day or so to see if the PCM readjusts.