1993 Chevy Truck our only mode of transportation

It may be fuel related, try spraying some ether into the air cleaner and see if it wants to start. Let me know what happens.

I apologize not getting back to you, I had some personal issues to attend too, but I am back now, so let's get to it. The first thing you need to do is put your old IAC back on the truck see if that resolves the issue, that truck is equipped with an electronic transmission if the speedometer does not work the transmission will not shift out of first gear it is called the VSS sensor, put that back together how it was with the old one and tell me what happens.

I was rereading your original response there's a few things I want you to do;
1. I have 5 different types of egr blocks that I can bolt in place of the egr, make yourself a little plate and bolt her on. Run it see if it changes The high idle, takes all the guess work outta it. While your at it throw the vacuum gage on the vacuum line to the egr and see if there's an issue with the control solenoid.
2. These engines run off from speed density. Do you have a vacuum leak, ie. Brake booster, egr valve, internal manifold leak, evap purge, ect? What are the counts on the IACV? Is the plunger all they way extended trying to make up for a leak? The easiest way to check for a vacuum leak is to get a small propane torch, do not light it, just turn on the gas and check around the engine and your hoses, if there is a vacuum leak you will know it or you can Pull the PCV, block off fresh air intake hose on other valve cover, and shoot some propane in the PCV hole. Watch for change in 02, STFT, or just listen for a change in idle. That'll tell you real quick if intake is leaking.
3. Sounds like the ECM is trying to control idle but cant and sets the IAC code. Either IAC has problem, or it is getting air from somewhere else like intake gaskets leaking or throttle body gasket leaking like stated before. Ive noticed in the past on these that the elec connector tab on IAC always seems to break off, I would make sure you have good connections there.
4. Check fuel pressure. If its on the low side of spec which I think is 9-13psi.

Engine runs unevenly at idle. If bad enough, vehicle will shake. Idle RPM may vary. Engine idles at incorrect RPM.
Possible Causes & Corrections:
Ensure throttle linkage and/or TPS do not stick or bind.
Ensure initial ignition timing is properly set. Check engine idle speed (both base and ECM idle). Check Idle Air Control (IAC) system.
Check for foreign material in IAC bore.
Check EGR system for proper operation.
Check park/neutral switch circuit. Ensure park/neutral switch is properly adjusted.
Check power steering pressure switch circuit.
Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter.
If rough idle occurs only when engine is hot, check PCV valve for proper operation.
Check evaporative emission control system.
Check for proper spark plug gap and engine compression.