[ChevyTech]

You're welcome.

There is a deceleration mode that holds the IAC open a little like a dash-pot on a carburetor. I believe the RPM, TPS and MAP signal are used for the ECM to decide when to bring the RPM down to regular idle.

The 0.9 volt reading in the data is a little off from what I would expect to see. I think the the spec GM puts out is 1 to 2 volts at idles. 0.9 volt could be out of the range it wants to see. The system could think the truck is decelerating.

Here is something you can try with the MAP sensor. When it is idling to fast, with a warm engine, bleed off some of the vacuum to the MAP sensor by holding the hose partially on the port so the vacuum is lower to the MAP and see how the system reacts.

The MAP sensor is interchangeable for many vehicles. Think of it as a electronic vacuum gauge. You could try swapping a MAP from another vehicle for a test.