What's your full list of mods? If possible I would take the adjustable fpr back off (if you have the standard) if you're only boosting up to 0.8bar on the ct9 you don't need the fpr. You could've actually experienced a bit of knock if playing with the fuelling too, if it was knocking it would pull the timing and loose power. Funnily enough mine was running like a bag of shit when I tried to MOT it earlier this year and it was just slightly lean, it struggled to get through the emissions due to that, with the CAT in too. As for the boost issue if it's the standard actuator it may be weak, a boost leak should show up all the time.