4x4 sapphire on P8 high comp, greys, air 2 air etc.

Car runs fine on tickover but under load cuts out, even if you press throttle sharply in garage it'll cut out, like it's missing at first but dies

I am getting 12v at ecu, coil, injectors etc when engine is running, have put new gpa coil, plugs,leads,cap,rotor arm etc in it and has a new enigne loom!!!!

what on earth do I try next????????????

any ideas / advice gratefuully received