Some questions. What is your fuel pressure? What injectors? What EECIV manual (A9L) or auto (A9P) or something else? Is it a manual or auto tranny? Do you have a VSS wired in?
If you are using a manual ECU with an auto tranny and no VSS you will get those stalling issues like you described. I had this issue when I switched over to an auto tranny. I switched to the auto EECIV and it worked good with no VSS. It still idles down pretty far when coming to a stop but doesn't stall. This is on a 5.0 though. How did you get the pip signal from the caddy ignition?