accelerator pump.

[IOWNATRUCK]

alright, so here we go, in park, my truck idles perfect, starts good, responds to throttle perfectly, no problems. now in drive, i can accelerate slowly perfect, sometimes i can mash the throttle down and accelerate perfectly, but sometimes if i mash the throttle down, theres a pop from the engine compartment, the engine rpm slows, and then raises and accelerates fine, ive talked to people and some say accelerator pump. well my carb is new, and it takes throttle perfect in park. now me, i was leaning towards something simple, like maybe bad gas, low gas (cause when i was driving it, it had probably 1-2 gallons of gas in it total, and the tank hadnt been cleaned so im sure there was 30 yr old gas and soot in there as well) are those possible causes of this problem? when i take the air filter off and give some gas, i see gas coming out of all 4 jets. sometimes it does it, sometimes it accelerates perfect, which made me think its not the pump. no vacuum leaks, or anything of that sort. its an edelbrock performer series carb. it doesnt happen all the time, and im leaning toward old dirty low gas. any opinions are appreciated man its bugging me ha,
Thanks.