my brother has a bone stock 305 sbc in his 84 silverado and we just put all new gaskets on and put it back in the truck, got it running and it idles fine starts up fine, but when you go to rev it up, you have to ease into it for it to rev up, if you just jump on and try and rev it up real quick it backfires through the carb, i checked the timing and it appears to be right, it points directly to #1 top dead center, i also cleaned his cap and rotor, it appears to be in good shape, im thinking its the fuel pump, we did change the fuel pump when we put the motor back in, and im thinking its giving it either too much fuel when you gas it hard or not enough, does this sound like a fuel pump problem?

i checked my vacuum advance, i left the rubber hose connected to the distributor and unhooked it from the carb and sucked on it and it held vacuum so it should be good, the timing i dont think is off, its dead on #1 cyclinder top dead center and runs smooth until i try and rev it up fast, im still thinking its the fuel pump