spray carby cleaner around gaskets, if idle changes you have a leak.
could be one of the vac lines off the vac reservoir under the plenum, bov source etc..
try removing vac lines to one turbo actuator at a time, just to make sure both turbos are in fact working, the power seems about right for one with a dead turbo.
Or check the two vac lines which leave the vac reservoir, one goes to the bov the other (i cant remember right now) but if they are mixed the bovs open under boost and limit power to about what your seeing.