True but I would check map sensor voltage with the two ecu's, it would rule out if the plug and play is using proper Mao sensor voltage, or maybe there the wires that need swapping, am unsure but am just throwing these ideas out.
Lol u do well to get 200bhp even with a standalone on a ct9, even if u did reach that kinda Power she would be blowing very hot and will not last very long.
Get a stock fpr and try or drop your fuel pressure below stock, a plug and play will be rich and it could be over fuelling and bogging it out on start up, u could also try check for codes, if not try the wires around it will only take a few minutes.
Put the stock fpr back on, what's year is the gt, as said above there is wires that need changed around if it's not the right model for it, I saw a thread about that somewhere.