Potential transmission issue

[EC2012]

Truck cuts out with AC blowing and in gear; turn off the air or shift into N and the truck idles fine. When cold everything is fine; once hot, accelerating in first gear sounds like when you first drive the truck in very cold conditions (higher revs without much movement) but will shift through remaining gears smoothly. Finally checked underneath and noticed the pan is hot to the touch; fluid is clean and smells unburnt.

Truck has 386,000 miles and do not know the service or repair history. IAC was just replaced, TBI refreshed with new gaskets and injectors cleaned. All TBI hoses and gaskets checked good.

The list of suspects seems to be fairly long, but I'm guessing the trans is on its way out. If that's the case a 4L80 is going in; I can get a remanned one cheaper than a 60. However, I will first go through the list to try and eliminate the trans as the culprit.

 

[EC2012]

Forgot to mention this; if the truck starts to stall, and you put it into N a few seconds too late, the truck will still idle down and stall. Starts back up every time. I thought replacing the IAC would have cured it, and it seemed to until later this morning after driving for a while.