Well I have the spring in the mail. So what you're all saying is that the spring helps this type of boost drop?
Does anyone know if the CPV spring from Dejon sets off any CE codes?
Don't want any unneeded trips to the dealer

 

No a spring will not cure this problem( dropping from high boost to 15 psi at high rpm). I have a dejon spring and as i stated before, this is called "limp mode" and can only be cured with another tune or boost controller.

 

Ok, not that one I understood. I have some other times when it will just not go over 12-15psi even at lower rpm's when I think it should be able to achieve full boost. 3500-4k rpm 3rd gear in"I" and comp mode expressway pulls.
Once it locks boost down to these levels it's tricky to get it back to 20psi. I am always trying different ways to revive it. Put in "N" and back to "D" or "I", turn Comp on an off sometimes even a key cycle at red lights.
I had to creep by an old mullet V6 Camaro race the other day because it would only boost 14psi. I'd have blasted by him at 21psi. I was

 

At least it wasnt a mustang. I have never had this problem with mine. I would suggest trying the spring. I just read a thread that stated after taking apart the wastegate the diaphram was collaped and this would never happen with a dejon spring.
My next suggestion would be (since this is not a massive boost drop) to check all of your clamps and make sure air filter is still in place and not loose.

If it will NEVER go over a low boost number such as 15psi at any rpm you have a leak or a sensor that is misreading.