Need help tuning Quickfuel carb

ive got a quickfuel super street series 680cfm vacuum secondary carburetor on my 300hp crate 360 magnum.
I’m running the Mopar Dual plane M1 intake and a 2 inch 4 hole carburetor spacer.
The issue I am having is a missfire that starts around 2500 rpm.
I’ve narrowed it down to cylinder 6 and cylinder 8.
At first I thought this was an ignition issue, I’ve replaced every last piece to the ignition and the issue still remains.
I’m rinning a brand new MSD Digital 6 box, a crane cams lx91 coil, brand new Taylor plug wires that have been ohmed for resistance and check out at 40 ohms per foot.
Brand new Ngk bkr5e plugs gapped at .040, a brand new firecore electronic vacuum advance distributor, new cap and rotor.
Timing is 18 initial and 34 total all in at 2500 rpm.
I’ve berified the accuracy of the timing
Mark on the balancer with a piston stop.
I’ve done a warm compression test on all 8 cylinders, I get 155psi across the board.
I’ve removed the passenger side valve cover and inspected the rocker arms and valve springs, no issues there everything is in tact and tight.
Since number 6 and number 8’s plugs are almost always carbon fouled I determined this has to be fuel related.
So I pulled the carb off and leaned everything out quite a bit.
I dropped the idle feed restrictors down from .031’s to .028’s.
Dropped the main jets down from 68s to 65s, dropped secondary jets down from 78 to 75.
I lowered the floats to the bottom of the sight glass. I replaced the accelerator pump cam with a white pump cam and replaced the squirter to a .028 from a .031.
All this seemed to help with the missfire a little bit but it didn’t solve it.
So I started calling around to different carburetor shops and ended up talking to a guy at AED performance carburetors.
He imidiatley asked me if I was running a carburetor spacer after I told him everything that I have found and what’s going on.
I said yes I’m running a 2 inch 4 hole spacer and he said to get rid of it for an open spacer because it sounds like a fuel distribution issue to him with how the plugs in cylinder 6 and cylinder 8 end up carbon fouled and the other 6 plugs look fine.
So I haven’t done that yet but I’m going too.
I was just wondering if anyone else had an idea for me.
I am at 3500 feet above sea level here in Montana, one thought I had is maybe I need to increase the size of the high speed air bleeds to delay the main circuit.
This thing idkes smooth and makes 20hg of idle vacuum, no missfires at idle, and it drives smooth below 2500.
Once you get to 2500 rpm it starts missing really bad, especially in 3rd gear, (automatic A-518)
So it seems when it has a load on it it’s just getting too much fuel and causing it to miss.
Idk what else to look at when the ignition is all brand new and everything checks out there.
And the compression in all 8 cylinders is great and I can’t find any broken parts in the valve train.
This has been stumping me for awhile now.
Carb is brand new too with less then 5k miles of run time on it and the engine is pretty new with only 30k miles on it.