missing at part throttle

having some problems ,i got a miss at part throttle , thought it was a carb problem ,tryed new one not it ... this is what i got

69 340
msd 6 box
new wires new plugs
mopar electric dist.
new cap and roter
headers
eddy air gap
holly 750 vac sec.
904 4.10 in the rear
electric fuel pump timing at 15 inital

my problem just happen it stumples at first quarter of pedal at wot it seem to be fine it get with it but at crusing speed it misses. in park holding it at a steady rpm like 2500 u can hear the miss and feel it ,kind like a flutting. any one got any ideas ?????