Got Shell 93 Octane and now barely idles 1973 Dart 340

You can't buy a vac leak at gas stations. :D
That sounds like restricted idle jets or water in the fuel to me.
Those carbs are pretty quick to pull the top off of a take a look in the very lowest spot in the bowls for water, but first I'd pull those idle air screws and blow some air through the holes just for kicks, and a possible fix. :D