87 Chevy TBI Stalling Issue

[Matt87chevy]

Hello! I have finally broken down and decided to ask for help after searching this subject numerous days.

The truck is a 1987 Chevy (v10) 4x4, 350 Tbi, 700R4 trans. I don't know if it is relevant, but it does have a decent sized sound system with 2 amps, which the alternator seems to handle fine. The A/C seems to suck up more juice than the sound system and seems to hover around 11-12 amps with the A/C full blast. (maybe irrelevant, but I thought I'd add that in there)

The issue I am having is a random stalling that happens only in drive gears (drive, reverse, etc.) Truck Idles and drives great other than this small issue.

Here is a list of what I've checked.
1. No Codes
2. No blown fuses
3. Brand new IAC installed yesterday
4. Checked for TBI gasket leaks and got nothing using the spray test
5. Checked the TPS and got the normal .5V at idle with ignition on.
6. Checked PVC valve and seems to rattle as if its not stuck.
7. I don't think its a EGR issue, because it only seems to happen at idle, I'm told EGR would affect off idle drive-ability, which I have none of.
8. I got my battery and alternator tested and they passed, even though they weren't tested when put into a drive gear. (should I have it rechecked while attempting to recreate stalling issue?)
9. Thought it may have been the converter staying (locked or unlocked?), unplugged 700R4 and the issue still happened.

I think that's all I've tried and will add more if I remember and other things.

Now what I'm not sure of and may need some answers on, other than troubleshooting the main issue.

1. Could it be a large piece of carbon where the IAC goes? It was hard to clean out thoroughly when changed.
2. Could the alternator not be keeping up the charge and causing the volts to drop low enough to mess up the distributor and cause this stalling issue?
3. Could it be a coolant temperature sensor? Even though this issue seems to happen regardless of engine temperature.
4. Could the distributor have lost magnetism and be causing this issue?(distributor was changed within the past 2-3 years) (read somewhere while searching and this came up as a possibility)
5. I was gonna try to mess with the idle screw, but I'm told that it will only adjust idle speed and not the idle RPMs, because the computer takes over and controls it. any opinions on this?
6. I am also curious if this could be a timing issue? When I changed the distributor I didn't set the timing with a light because the (timing marker thingy?) was gone and we did it the old fashion way of turning the distributor until we heard knock. We also didn't follow the correct timing procedure of unplugging the computer and putting it to 0* TDC and then plug it back in the give computer control back. (sorry if that was hard to follow, I'm tired of thinking about this issue.)

I'm at a pretty stagnant point here and am pretty stuck on trying to figure this one out. Any help in this matter would be greatly appreciated and if you need any more info I will try to get it to you as quickly as possible, thanks.