01 5.4 idle Issues

Kinda at wits end trying to find my problem. I know many posts have covered this problem, and I think I've tried just about everything people have suggested.
My truck has 234K miles and it runs so good when its warm outside. But when its below 30 degrees like it is now in MN, it has trouble idling (still runs great at higher throttle). All indications, including STFT and LTFT point to intake leaks, but I have tried everything including spraying starting fluid, and I can't find anything. Have also changed IAC and EGR with no change in symptoms. PCV valve has been replaced, and the entire PCV hose assembly has been removed and inspected, and it has none of the usual deterioration. I have the newer style manifold.
When you first pull up to a stop sign, it will idle down to about 650rpm or so, and then after varying amounts of time will either quit with no warning----or start stumbling around like its going to quit. You're never really sure if its going to act up or not, or which way it will act. But if its cold, it eventually will act up. I have resorted to putting it in neutral at every stop sign----a real pain in the butt.
Sorry to make such a novel out of this, but I wanted to tell the whole story in hopes that someone will have a suggestion I haven't tried yet. Hard for me to believe that a vacuum leak would have so many faces. You'd think it would be the same every time. How can a bad hose or gasket make it quit in the blink of an eye one time, and then give me the stumble around program next?? Does anyone have an idea of what I am looking at here??