For the amount of fuel loss you're describing I would suspect you have a sizeable leak somewhere!
Turn the boost down, remove the FCD and report back your findings, my suspicion is the FCD is cocking up the map sensor signal to the point where it's just dumping fuel in because the poor ECU doesn't have a clue what's going on.
If you want to run higher than fuel cut you'll definitely be needing a FPR, at the very least buy a gauge you can plumb into fuel line to check fuel pressure.