Hi mate welcome &sorry to hear about your troubles, easiest thing would be to get it on a dyno, that will give the best indication of what's happening or not as the case may be,
If ecu is upgraded it's either a standalone apexi or has an els board or one has been put in from a later model, how many plugs does it have ? The boost issue could be anything from a split hose to more serious problems, best off taking loads of pics and posting it all up, we're all friendly here and will try to help out as much as we can