351W THUNDER

car runs mint after 2,000 rpm.. let it idle then hit the gas nuthing just boggs then kicks in. just rolling then getting ready to go sumtimes it works sumtimes it hesitates like a bastard.. the car starts right up tho.. what could be the problem. thought it was the gas so i put dry gas in... still did it so ran it out of gas filled it up with nice fresh gas and same problem.. any ideas!?