I would think a hesitation/dieing/stumble would be lean (vac leak) & this sounds like that as opposed to a blown PV which would put you on the other end of the spectrum which would be the power circuit would then be on full time & be too rich. (unless a blown PV stays "off") but that still would not make it hesitate/stumble at less than WOT throttle, it'd be like normal part throttle operation when you are on the "cruise" circuit.