1990 Suburban dies intermittently

[Dale99]

I will say pull the TB off, and clean the IAC and its passages. Be careful not to spin the tip of the IAC while its out.

A stuck open IAC will cause stalling and whistle.
Open EGR can cause the O2 sensor to read rich and cause codes(possible whistle as well).
code42, you also have whats called a pickup coil in the distrib, its basically a bunch of wound up copper wire. I have heard of them going bad... not often though.