Seams like the boost is being bled off. Are your valve spring stock? I wouldn't be running that power on stock springs, they float at high rpm causing power lose and the car will then idle like crap for a few seconds. How did the tuner shop make the actuater bracket, just a long shot but maybe the flapper which is connected to your actuater is not closing due to incorrect bracket which will put the actuator in the wrong position. Check everything mate, where did they plumb your boost nipple? What BOV are you runnning, maybe the spring is not strng enough and when you car build boost it bleeds off? Either way a boost leek you would be able to hear.