help with engine bog/misfire

[Blackbird66]

I have fallen into a black hole from hell..............
Problem: Engine bogs/misfires between 1/4 and 3/4 throttle. Idle is good with around 18 vacuum. Engine runs great pass 3/4 throttle as carb transitions to secondary. Spark plugs are white, and problem is worse as air temps drop. ( This means lean)
I am running a 350ho crate motor with holey 600 carb jetted to gm recommendations. 10 degrees advance on unilite with Malory coil gaped .040 My spark seems weak, but that should effect full throttle/ high rpm and not low throttle low rpm right?
Anyway, I can find no vacuum leaks, nor any problem with holey. I tried a new edelbrock 600 last night, and it ran the same. I don't see how I could be so extremely lean, my tune should be very close.
Ideas?
Thanks, James