Seems like if the car would not go rich, you would need a larger fuel pump and/or injectors.
Have you changed them? Since yours is a 99, you have 26lbs injectors. I know my friend's injectors were maxing out (same injectors in 2000)
Glad to see you got more power. I had a 150 shot with just a lid and catback and made 390rwhp and 515rwtq on a Mustang dyno.