1991 Celica GT - Starting Issue

[Aphelion2012]

Alright, to begin:

1991 Toyota Celica
Toyota 2200 Engine
Cold Air Intake
Custom Exhaust from the Cat back
Glass Pack Muffler (cheapo 'Cherry Bomb' which im half tempted to hollow out at this stage)
Custom Distributer/Rot/Wires
New Injectors
New Fuel Pump
New Fuel Filter
New Timing Chain (belts be buggered)
Oil Cooler
New Igniter
New Ignition Switch

Automatic (yeah, yet to get around to changing it out)

And now the bugger wont start.

Driving it one day, it decided to keel over at a red-light, but started right back up so thought little of it. Over the next few days it did this more frequently until, now, it wont start. (Save on rare occasions) No sluggishness, no backfires, no lack of power. I've checked the following:

Timing
Cap/Rotor
Spark
Fuel Pressure (besides, when it does start it can tac out with no problem, and dies again when the RPMs drop)
Oil Pressure
Compression

I just replaced the O2 sensor today, so I'm assuming its either the ECU or the crappy glass pack has gotten clogged. Figured I'd ask before I took a breaker bar outside and created a straightpipe out of my cherry bomb, or bought a new ECU (which I need to do anyway, but dont want to right now... besides, everything else functions fine.).

Edit:
I have now also replaced the:
Coil
Fuel Pump (again)
Fuel Filter (again)

Its trying, its just ... not going.