have you tested/adjusted the TPS?
I would take the IAT sensor out and clean it too.
When is the last time the fuel filter was changed? Fuel pressure check pry wouldnt be a bad idea either.
If all that checks out, maybe your coolant temp sensor is bad. It will tell the ecu it is -40* and will run rich, we had that problem on another forum.
http://www.cherokeetech.com/VBull/sh...-Starting-Hard

 

I have not adjusted the TPS, and I have not checked the coolant sensor. It didn't occur to me that would be relevant, but I will check it out.

What is the IAT sensor, and where is it located?

 

Make sure that map sensor is getting manifold vac. You can pull the line off it and feel it with your finger. Wrong or leaking injectors? All I got.

 

Just for kicks, i would pull the distributor and make sure the engine is timed right. Sounds like the problem I had when i had the engine timed wrong

 

I was wondering when someone was going to mention that.

Another thing to look for before you pull the distruibuter is a crack in the distruibuter cap and cracked plug wires. Start it up and look at it in the dark. You might see a nice light show.
In my experience you will get these symptoms when the engine is under load and the spark parts are failing.