Let'* clarify what you've posted already.
The engine does or does not turn over with the starter? You mention it wants to but won't (Check battery cables at both ends for any corrosion, possible you have full power, but can't get enough to the starter)
Shouldn't be plugs or wires or alternator if it ran 100% just before this happened.
Check the resistance on the coils per the techinfo article. Start with the posts, if you get odd readings pull them and check the primaries.
Take the connector off the ICM and look for any corrosion or issues...ensure everything is making good contact and reinstall. (sometimes taking off and putting a connector back on 5 or so times does the trick to clean up contacts)
Most of the info I got was because you mention a stumbling. It could also be fuel pressure related as well. A fuel pressure gauge hooks up to the valve on the fuel rail to give you the reading.
00 Regal GS: All kinds of cool stuff.