[FWB]

your running out of fuel some where, what size fuel line? is the fuel pump still
supplying enough volume when your at 3\4 throttle? what holley pump is it?
16psi isn't necessarily the only spec that is pertinent. what gph or gpm is it?
or.........are you dumping too much fuel,...... after a blast check the plugs,
secondaries might be too much for the motor.....if your runnin at 60 mph and you dump it does it still have a flat spot?