Well, for what it's worth: when I had the exact same symptoms on my veg side I could diagnose it pretty easily because I have clear fuel lies after my 3 port valves. I had an air leak in my filter connections and when I would switch to veg I could see the bubbles in the line and the car would display the exact same problems you described: loss of power and eventual stall.

Try clear lines as suggested in a previous post (if you haven't already.) It sounds like air to me. Clear lines really give you a window into the fuel going into your IP. That is, you will be able to see immediately if you have air and where it's coming from -good luck.