Flash build stuttering

I have very annoying stuttering effect in Flash build. It appears as short-time but really heavy framerate drop, happens periodically. Editor and webplayer runs smooth at 400fps.

Probably it is Garbage Collection, but i have done many things to get rid of it and dont see it in Editor using Profiler for now. Actually i am not instantiating anything during gameplay, just using pools for some objects and thats it. Also, not using OnGUI at all, nor GUIText etc. I am using NGUI (it eats huge amount of frame processing time, that scares me, but i dont see spikes).

The question is - how can i profile flash build and find out what happens during this fps drops/pauses?

You can profile your Flash build using the profiler in FlashBuilder (create a project to load in the unity swf as per the preloader example on the forums). This will show the memory usage and live objects so should help determine what is causing your framerate issues.