Are these venom injectors supposed to be direct replacements for the stock ones? I understand they're 19 lb, but there is more to an injector than just the flow rate. What pressure were they injectors rated at? Was it 19 lbs at 3 bar or 4 bar? Are you sure they're all connected properly?
Also, what brand of sensors did you replace everything with? Unless you know for certain that the MAF was bad, I would swap back to the factory one. The aftermarket ones are generally garbage, and your MAF airflow table would likely need tuning for it.
What brand is the IAC? Again, unless you can prove the factory one was bad, I would swap back. If the issue started after the injector swap, then there is no reason to assume the IAC is the culprit.
Are all the grounds connected? Wiring all good to the IAC? Do you have something you can datalog it with? If not, probably get something.
I would be really interested to see what your TPS is reading, and also what your IAC position is at when starting. This doesn't really sound like a fuel pressure issue to me.
After the crank and cam position sensors are changed, and crank relearn procedure needs to be done, but I don't think that would make it run like garbage, just throw a code.
Also, are you sure the distributor is installed correctly?
http://www.gmtruckcentral.com/articles/distributor.html
