Timbo

What I do is get this extension harness.http://www.wbodystore.com/IAT-Extension-Harness-p-65.html I then use a 1k resistor inline with the switch to just jump across the 2 wires.This way when the switch is flipped one way, that circuit is open and the ecm is reading actual iat temp. When you flip it the other way it adds the 1k across the two wires lowering the total resistence thus the ecm thinks its hot and pulls timing out. In cold weather, it starts much easier when the ecm gets the actual iat reading to advance timing for cold start.

I would fool the iat circuit, I have fixed a few trucks with that very problem with a 1K resistor in the iat circuit. I actually had that problem with my truck and beat my head against the wall trying everything and that fixed it. Some trucks with big injectors and timing boxes it happens. With my edge on, below 55 deg out it would do it. It would also be a good idea to put in a 190 thermostat. Timing seems to be the issue because my smarty with no timing. there was no miss. The ecm thinking its hotter pulls timing out. Its worth a try, about $2 at radioshack.