Having a similar issue with my ED30. Seems to pull well when cold but when up to temp, after second, boost drops after around 3500RPM.
Car has just been serviced. I mentioned the boost issue beforehand and they kindly took a look for me. No codes or low boost pressure reported but they did notice that part of the wastegate actuator housing was rattling around along with the actuator rod. I haven't taken the car back in to have this looked at yet, but the mechanic seemed reasonably sure this would be the issue.
Like the OP, the lack of boost is an intermittent issue.
Not saying that's the problem of course, just offering another 'may be'
Will post back here once I've had the work done to repair this to comment on whether or not it fixed my boost issue.
