You shouldn't transition till 4500 RPM. After that, if you don't get full boost there is a problem. Unfortunately, I NEVER had a boost problem in my car, so never had to diagnose one, thus resulting in my not knowing what the hell I'm talking aboot. I do know that after transition... You should be back to full boost in NO TIME!

Yea sounds like maybe you have a sticking actuator?

Hard to say really. You'll just have to go through and check all the lines/solinoids/actuators one at a time.

There is no sure fire answer to your question.

Chasing boost gremilins is not always a straight forward task.

Well it sounds like you have the mods to run your turbos parallel. I have found it much easier to do any trouble shouting with boost just be running my turbos at the same time. Stock you have god knows how many boost lines but if you run them parallel you end up with like 4 boost lines. This might be sumthing you would want to look in to after you find out what you problem is. I wish I could help you but they are right ther is no way of telling what is actualy going wrong. You will have to look at everything to find out. Sorry.