Thread necro aside, you are mistaken.You do know the Corvette has the PE button and circuitry to use PE mode.
The Impala/Caprice/Roadmaster does not, so without fabrications to the circuitry and a switch, PE mode does not come into play when tuning on a non corvette model.
If I’m mistaken please correct me.
If conditions are met, the pcm will enter power enrichment mode. Can't say I've ever heard of a switch to enable PE.