I know you say there's a problem from 5-7k rpm but without you saying that I couldn't tell from the video. Things seemed fine in the video.
To recap, you're building about 8 psi with the boost controller hooked up and fully tightened? If you remove the boost controller and put the vacuum signal directly to the wastegate actuator you build a little less boost maybe 7 psi? Then if you take the wastegate actuator bar off of the wastegate flapper and you make 3 psi?
What happens if you leave the wastegate actuator rod connected to the flapper but don't run any vacuum signal to it? Have you tried that? If so, let me know what happens. If not, try it (but be careful not to overboost).