I am thinking timing,I would check stock harmonic dampener for slipped outer ring. If ok.
I would still add some INITIAL timing up to 15, tune distributor curve for 35 degrees at 3000 rpm, add as much vacuum timing as it will tolerate for cruise. Then start chasing carb issues if any.
In my experiences when carb acts finicky at idle tune distributor for best vacuum, adjust carb for best idle.
One other thought, I have seen multiple edelbrock timing chains installed incorrectly due to vague 0 degree timing marks on lower gear. If you didn't use one of these sets no worries.