Slant 6 hesitation or stumble

I have a 1965 dodge dart with a slant 225 slant 6 with a Carter 1barrel carb and points distributor . The during warming up and after fully warmed up has a good even idle with no miss. When i go to give it gas it stumbles/hesitates then picks up? I've checked the timing,points and points gap and fuel pressure.i use fresh 91 octane no ethanol. I took my time and fully rebuilt the carb including cleaning out all ports and passage ways and no fuel leaks or vaccum leaks ? The only thing i can think of is the vaccum advance or it could be out of adjustment from being on the car for many miles even thought i bought it remanufactured from O'reallys . What's your guys thoughts? Thanks