Well, I can't speak for the boost creep problem but I have seen enough cars to know that just because the fuel pump is working, doesn't mean its working properly. I would take it out and seen if its a standard pump or uprated. If its standard then its more than likely the first day pump and never been replaced with a new pump. It does happen but I personally have never seen a fuel pump just stop working, they just slowly get worse and worse over time. Without actually seeing the car it sounds to me like the pump is working but when it comes under heavy load it can no longer cope with the demands of the engine which is why the tuner had to bump up the fuel pressure to such a high level in order to compensate.