I've been chasing this issue for a couple of days now and I'm not sure I'm on the right track, maybe I'm over thinking it, but any input you guys have would be much appreciated

Vehicle: 1990 K2500 350tbi th400 8800lb gvw (8 lug truck)
Stock tune except for timing bumped up in the +1000rpm range and smoothed fueling tables. All stock long block.

(I'm ruling out the tune because it's been starting idling and driving great for months now)

What it does: Past couple days have been cooler here in NC, in the 30s. On a cold start first thing in the morning it will crank fine but will not fire. It will start only if I hold down the gas pedal and feather it a bit. Once started it will barely idle, it will hunt and sputter between 400-600 unless I hold down the gas. It will not fast idle. If I stop holding the gas it will chug down to 400 rpm until it stalls. I can hold the gas down and keep it at 1200ish rpm to warm it up, as it warms the idle will smooth a bit until finally it will idle and run on its own normally. It drives normally after that, and I can shut it down and restart while hot without issue. While I was diagnosing I also noticed it would hunt at idle a bit, bouncing around 1-200 rpm occasionally. After messing with it the problem has inexplicably stopped and the truck is running and starting great again.

Initially I was thinking a bad IAC, but it may just be sticky because I've been unable to replicate the issue and after testing it and reseting it it seems to be functioning normally. I attached a quick snapshot of tuner pro right after I started it this morning while I was trying to get it to act up. As far as I can tell all sensors are reading normally. I diagnosed for about 2 hours last night and all the data read and looked the same

I did notice the TPS voltage did bounce between .51v and .53v and idle causing the Tps% to bounce between .2 and .7. Not sure if this is normal or could point to a failing TPS.

I checked for any vacuum leaks and even blocked off several ports but the problem went away before I could verify anything. I shot some carb clean around the base gasket and vacuum lines, no effect. I put everything back to normal and it's still functioning correctly this way.

I still lean toward sticking iac, I ohmed the pins on it and read in spec at 50ohms through the coils and infinity across. I checked the connector with the A and B ALDL pins jumpered and got voltage into all of them so it seems to be working correctly as well. I'm debating cleaning it but if it's being problematic I'd rather replace it. Maybe I'll pull it and look at it, but from the looks of the end of the pintle I could see from the top of the throttle body it didnt appear dirty. I rebuilt the TBI a couple years ago and cleaned it all then as well.

My other thought was EGR sticking open, as I did push open the valve while it was hunting to see if that affected it, but it did not seem to as it idled worse when I opened it. It's possible it was a a little sticky and I freed it up but it did move smoothly and easily.

Fueling wise it has a new ac delco EP381 pump and injector spray pattern looked pretty good. Both pulsing cones. Pressure I didn't check but after I put the pump inot it was rock solid at 13psi.

I checked timing, it was good at 0* with the ESC plug disconnected.

I'm hoping it acts up again long enough that I can pinpoint it. Right now I'm leaning toward iac, maybe egr like I said. Let me know what you guys think.