motor running like a pile of......

just cant figure this out myself
engine runs rough up to about2300 rpm during low load as soon as giving more throtle it runs nice and smooth from 2300 and up runs very smoth, except about 3500rpm and up when it starts missing almost like ignition is turned of or running out of fuel just a fraction of a second then power comes on again (but week) and then missing again very frustrating have tried pulling it up to about 6000rpm this way , i know its not right but things happen pretty quick when floring the loud pedal..
responds nice and quick reved in neutral
motor is a 11.9:1 compresion stock stroke 340 with ported eddy heads small compcams solidroller ( 242/[email protected] and .570/.576" lift )
now it has a rpm airgap intake..
msd probilet distributor and 6AL box
750 proform dp carb (have tried two of them since i have another one)
carter mechanical high volume fuelpump (about 3years old have checked fuelpreasure at idle)

have changed wires ( they are all in betwen 74 and 114 ohm)
new cap and rotor
changed old 6a box for new 6AL box
have done leaktesting with motorstarter gas and no leeks anywhere
changed all sparkplugs, did find one with cracked centerporceline but would gues thats just a "monday misstakeproduct" since all the other ones where fine motor runs alitle fat but not crazy fat)

cant even do a burnout with this:( even with 3200rpm stall and 3.21 gears(gears will change)

help:S need to get this thing running as hard as it should so i can start playing with the nitrous.......