I'd look at all the small things first before spending any more $$$, wiring, fuses, earth straps, coil loom, fuel pump wiring and fuel pressure, 0.8mm spark plug gap, clean AFM, O2 sensor, injector clean etc etc etc These things can drive you bats finding them.
Also try this: http://www.skylinesaustralia.com/forums/St...er-t233110.html