[AZKen]

Well this website is not for GMC's with Cadillac motors but if it's an electrical problem maybe we can help.
Let me know when you have redone the connection cleaning and tightening.

The change if the wheel has no bearing on your issue. As you say there are many possibilities for your trouble, but first things first.

You have an intermittent electrical issue it seems. That usually spells connections. When the whole system is dead.... it spells big connections. So focus, clean and tighten the ones I mention again more carefully.

The very next thing is take battery to get it tested under load. Tell us what they say about the battery.

If you want to get a remote starter switch or jump the starter, go ahead. This will eliminate or expose ignition switch and wiring.
Do another check: Key off, turn on headlight switch to see if they come on. If they do, turn key on and crank motor, observe what the headlights do.....dim a little or go off? Did starter crank motor? Headlights won't come on at all?