Clean the IAC motor, located on TB, take it apart and spray it with brake clean/carb cleaner is what I have done in the past. You can also get a can of carb cleaner and spray around the vaccum lines, listen for the engine changing tune and you might be able to detect the leak that way. Usually it does mean the gas cap was off, but it also could be a large line as well. Sometimes on the dodge vehicles the one on the brake booster is usually the culprit. Let us know how it turns out.

I would think if it had a vacuum leak large enough to make it stall at idle it would have lean codes stored in the PCM as well.

Well you were right problem fixed.