Believe it or don't but I just went through the exact problem with My 472 Hemi I changed carb..new fuel filter..new high flow fuel pump...cleaned all the paint off the orange box and fender to get a better ground..none fixed it. A friend told Me to check the alternator as He said it might not be putting out enough at low rpm. I checked the alt and it was good but noticed the belt was not as tight as it should be. I tightened the belt and have no stalling at idle any more. And that's the truth.
I am glad you found a solution
But electrically, it does not make sense. If the alternator output was low, the battery should have supplied adequate current/ voltage to compensate for the low alternator output. The exception being the battery is very weak or there is a problem elsewhere in the circuit. In that case the Alternator could back feed the circuit to mask the root cause
