Have you not just changed your downpipe?
As far as I understand it, the limp mode has nothing to do with the boost you are running, but all to do with what voltage your maf is reading. Hence why some people can run 20psi and some limp out at 15psi.
If your downpipe is in, it is that, if not, it could be the maf. But as rob said I would adjust the boost setup first.
I'd start with the needle valve as it seems it will be your spool up that's changed with the downpipe having a lot less back pressure.