Im betting on the iac I've been told that three times so far and when i told the very helpful gentlemen on blazer forums abotu the vacum being good and it actually workign better with a huge scale vac leak he thought it was the iac.
im not sure if i can test it or not but im going to find out today!
and i dont know anyone that has that system. and i've been told and i read in the haynes book if its not one of the sensors you recomended outside of faulty electrical connections its either the cap or plugs are bad or were installed wrong or feul pump but that has been replaced prior to purchase. i was also told and read it could be cam shaft wear but i doubt it it only has 114k on it and a ex state police officer owned it and he wasnt a speed demon!
heres the forum where i was told the iac
http://www.blazerforum.com/m_172755/mpage_1/key_/tm.htm