How about we start with checking for diagnostic codes?
http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx
It seems the accepted rule of thumb with injectors on OUR engines is desired HP + ~20% overhead. Sure, a 550 CAN do 500RWHP, but it's at a higher duty cycle than most injector manufacturers will guarantee (most people you talk to will recommend 650's for 500RWHP). Flow ratings are peak, not the max sustainable flow.
EDIT: Oh, and if you're running so rich you're shooting fireballs, I'd completely forget the fuel filter and expect to spend time troubleshooting the knock sensors and ignition system.