Full throttle hesitation

[mikajo39]

OK so I got my new engine in my truck and it's doing prety great,problem is though, if I drop the hammer, it'll stumble and bumble till you let off and try and ease it into full throttle. I tried adjusting my carb (edelbrock 600cfm 1405) accelerator pump for a bigger shot of fuel but that killed it entirely, then I went to the smallest shot of fuel and once again it died. Otherwise it runs great. It's a mildly hopped up 355 (cammed, headers,vortec heads,year one crate motor woo!) with a GMPP HEI, I have the vacuum advance on the full manifold vacuum side. The problem is with the distributor is the vacuum advance can it's so big (in size) that it hits my intake manifold and I can't adjust the timing much without the can hitting , and I must be having brain fade but which way do you turn it to advance or retard. so do you think its a fuel problem or ignition? thanks in advance!