Well, I'm personally at a bit of a loss, becuase it sounds like you've pretty much replaced the entire TBI setup already, lol
It has to be either a vaccum leak somewhere (not all intake leaks are external, some come from the lifter valley, and the carb cleaner trick won't work) or an adjustment error with regards to the throttle body.
I personally would consider the throttle body to be the most likely culprit. You should try the following to set minimum air:
Grab yourself a paper clip, and bend it into a C-shape. You'll want to go to your truck's ALDL terminal, and ground the orange wire with the black stripe to the black wire with the white stripe. Turn your ignition to on, but don't start the truck. Your Service Engine Soon light should start flashing codes.
The Service Engine soon light blinks a bit like morse code to tell you what is going on. It flashes each code three times, before moving on to the next one.
You should get a code 12 first. To figure it out, watch how the light flashes. It will flash each digit in the number individually, it is up to you to know which is the first digit, and which is the second. It flashes each code 3 times before moving on to the next one. For example, code 12 should come out as "flash........flash, flash....... flash......... flash flash....... flash..... flash flash......" One blink for the 1, then two blinks for the 2 in 12.
So, assuming you only have an EGR code that you know about, it should flash 12 three times, then flash code 32. If it flashes any other ones, let us know.
While you sat around watching the SES flash, your IAC has been busy motoring away, closing off the IAC passage in the throttle body, assuming it can. Go to your engine, and unplug the IAC. Its the big round cylinder coming out of the side of the throttle body, and has a 4 plug connector.
Then go into the truck, turn the ignition off, pull your paperclip out, then go and try to start the truck. If it won't start, your problem is in your minimum air adjustment. There is a throttle blade adjustment screw just like a carb has, except it is a torx bit. Often there is a small aluminum plug in there to discourage people from fiddling with it. Use a punch to knock it out, then open the throttle blades 2 - 3 turns by turning the screw clockwise.
Go an try starting your truck again, it should fire right up, and idle fairly high. Wait for your engine to get up to full operating temperature, then back the idle screw off so the engine is idling as low as it can smoothly with the air cleaner still installed. No good setting it to 350 rpm, and having it missing / running rough. Usually this is between 450 - 500 rpm on a stock TBI smallblock. After you've finished your adjustment, shut the truck off, plug the IAC back in, then unhook the positive battery terminal for a minute to erase both the EGR code, and IAC code that will be set.
Start the truck up, and see if that is any better. It should fairly quickly settle down to a 650 rpm at full operating temperature.
If not, you may have an internal vaccum leak.
Is this engine totally stock? Or have you made any modifications that caused the problem?
