My other car is a MINI!!!!
It's not a mapping issue you've got mate, it's a hardware problem.
A map is fairly straight forward, in so much that if it worked when done, then it's still working, and something else is at fault.
It sounds to me like you've got a pipework issues related to either your N75 or DV. Either from when you've been changing your DV over, or just a natural split somewhere in the system.
Where abouts are you? It sounds like you've already spent a load of money on parts you didn't need, so I'd suggest you find someone who knows these engines well and get it looked over properly, and by that I don't mean an average joe garage, but an enthusiast from the forum or specialist tuner like Rtech themselves or Badger 5 or similar.
It'll almost certainly be an easy fix, and from what you've described, I bet it'll be easy to find as well!