Interesting thread because I'm seeing the same thing on my setup. (low HP / Torque, peak boost of 21 psi at 4k)
Dom 1.5 w/10cm hotside
Killer B headers / Uppipe (Wrapped)
AVO Mid / Y-pipe (tapers to 2.5) but still have the stock mufflers.
Process West TMIC (Gold wrapped)
KSTech 73mm CAI
Honestly I don't know how people are making so much power. I got it protuned at two different places local. First place made OK power, but DAM was consistently 0.81 and AF learning D was -15. No known boostleak, but tuner wasn't responding. Other place was tuned during the heatwave (100F) and made ~300/~300.