Very much it sound like the problems are to do with the restrictor pill or the lines as i had the same issue many years ago with 97 wrx and only made 7psi on a dyno day, embarrassing. But i would double check the intercooler holds pressure as they do fail on the odd occasion.

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Motec
HKS 2835
Whiteline Group 4 Coilovers
Was 227kw 410Nm
Now?