[sea dog]

Icm is built into the coil modules for ls series engines. Have you checked the ground distribution for the coil packs? And all the engine and pcm grounds as well? You know that 6.0 iron block engine was in a 2000 formula. But seeing that it's not the original engine to that 2000 formula, what year, make, model did the 6.0 come out of?

Since these cars use an electronic throttle control, have you checked to see if it's working correctly?

I would put engine on an ignition oscilloscope. This is the most reliable way of knowing if spark is good enough to run engine. If you don't have access to one, ebay has a pc based single channel pc based scope at a reasonable price. This would not be a one time use tool. Everyone with a newer coil pack car should own one.

An obd 2 scanner that does real time sensor data would be a good thing to use also. Even with ignition on, engine not running, or engine cranking will produce much useful sensor data. As an example; a failed map sensor, if ls series uses these, would show very low or high voltage while cranking. Low voltage would cause pcm to over fuel engine while high voltage would cause very lean fueling.

Your fuel trims while cranking should indicate weather pcm is over fueling engine.