Boost issues 1.9pd

Wonder wether anyone can help, I've got a new gtb fitted to my car from xman a GTB17/60 and it's not making full boost until 3500rpm and a stock 2260 makes full boost by 2500 so I've a problem somewhere..

John (faboka) thinks I've a vacuum problem so I've currently got a mightyvac on the actuator hose pulling 16inhg and I'm gonna leave it like that for a while to see if its the pipe.. Is there any other pipework from the vacuum box I should be checking that could cause problems?

Could it be the vacuum box itself? Any way of testing that on vcds? Or does anyone have any ideas of something else it could be?

Thanks