Lights flash after starting

I have a 96 4X4 Jimmy SLT with 115000 Km on it. Sometimes when I start the truck all the lights will flash on and off for several minutes. It sounds
like the 4 way flasher is working as well. Dash lights, signal lights all flash. If I just sit there and rev the engine a little they will stop after a few minutes. Does this have anything to do with charging from the alternator? Battery is good, terminals are clean and tight. Anyone have any ideas?
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