1 of 2 things is falling short. Air or fuel.
Is it possible the air cleaner or intake pipe are collapsing? Im guessing no because you have a 85mm maf. You prolly have a solid pipe and a k&n filter. That leads us back to fueling.
In my experience with weak fuel pumps, boost will rise then fall off specially in high gear. A fp gauge can be deceiving. As boost falls off so does fuel pressure. It's hard to determine what's happening first. Is boost dropping due to fuel pressure or vice versa.