[StylinPro]

I'm no turbo expert, but I'm thinking more exhaust volume with your new system translates into reduced velocity which translates into reduced turbo rpms and less boost...

True, and check for leaks in what you installed as well, never know you might have thought something was tighten down and turns out it wasn't

 

[StylinPro]

I had a 2011 ECO 6MT - installed a Borla cat back. I had the trifecta tune - would hit boost in the 20+ psi range. Did notice in summer temps boost was higher by 2 or 3 psi then in winter. Has to do with air density. Did outside temps drop significantly after you installed the exhaust?

That's strange, colder air should have higher psi rather than warmer air..hmmmmm