Thanks for the input. Verified the timing chain is fine, checked ignition module, coils, new plugs and wires, new intake manifold gaskets, fuel injectors verified OK, new ECM, O2 sensor, crank sensor, fuel filter, etc. Seems to be that the ignition circuit is not getting consistent power. I'm thinking now that it could be something in the ignition switch or wires in the steering column. I bought a Tahoe cause I needed something that ran. Hopefully I'll work on the Lumina again in a week or so.