Sorted the boost issue, i had removed the filter inline to the MAP sensor as it blew off on boost, put this back in and no more problems with it holding boost.
However the car still holds back quite badly as the engine 1st comes on boost 2.5k rpm - if you hold it at 1/4 throttle it pulls through it and once its cleared at around 3.5k rpm it drives fine after that! Fuelling issue maybe?