hello i have a chevy 305 engine that has a 600 holley carb everything else is stock,and the problem im haveing is like loping or surge and wanting to cut off in gear.it runs fine idleing i cant find a vaccum leak but when im driving and i gas it hard and when i let off the gas it seems to want to stall for a min until i get back on the gas,and its a center bolt headed engie im stumped it runs good highway and cruising its just in gear it wants to cut off or if i come to a red light.