Am I right in saying that the boost hose connections are the 2 lugs and a U shaped clip type?
I don't know if this helps, but they get weakened by playing with them, thus allowing the connections to pull apart under boost and leak out. This in turn throws the ECU to cock and may be your problem, as Jonny has alluded to..?
I had this problem on my 150PD - you can't seperate them by hand, but a shed load of boost soon forces them and it's very difficult to diagnose.. as you can't go nosing around under there with it on a rolling road trying to replicate it.
Pig of a fault, but re-tracing your steps to last known working configuration (oh, there's the IT in me) seems the next step.