Get a battery/alternator test at autozone. Are these the only devices that are losing power? What about radio or interior lights? It could be a poor connection. Or as you say, ignition switch.
Start with the easy things. I would try putting a voltmeter across the battery terminals while the problem is occuring. It should not be changing much, if it is alternator is suspect.
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'99 GTP, L36 bottom, XP cam, Headers, 3.29 gears, FWI, Powrtuner