Still haven't figured out the idle issue...

So a few months ago I had problems with my '68 missing and all kinds of nonsense..turned out that issue was a faulty ignition coil and wonky ballast resistor. Got that figured out, but there has been an ongoing issue with idle quality pertaining to fuel mix. I'm running idle at about 850 rpm, vacuum is 20 at idle, with 5 degrees of advance. Valve lash is .12 and .22. Anyways, if I set the idle screws on the Holley 390 for best idle, there's a huge dead spot as soon as I start pushing on the gas, and the motor leans out enough that it usually stalls. If I set the idle pig rich so that the motor surges, the dead spot obviously goes away. But then the idle sucks. So the gist is that I have to sacrifice idle quality for driveability.

So what should I be looking for? I'm almost sure this is a carb issue, but what in the carb could beccausing this? Is it possible that this is a power valve issue?