Hi mate, you say it does not feel like it is giving you full boost, that may just be your problem, I am afraid that most of my knowledge is with the classic Impreza but this would be worth checking out, if your boost control solenoid is not working/cycling, it remains closed which allows your wastegate to open @ roughly 0.5 BAR (on the classic anyway) you will not get a Check Engine Light but your boost will be limited to 0.5 BAR, do you have a boost gauge?
Cheers Iain