Misfire at cruise, popping/afterfire at 3000RPM

Your engine has FOUR important timing milestones. In order of importance, they are;
1) Power-Timing
2) Stall Timing
3) Idle-Timing
4) Cruise Timing
All except #4, ARE DONE/MEASURED WITH THE VACUUM ADVANCE CANISTER DEFEATED

Step-1
When you check/set the Power-Timing; you rev it up in Neutral/Park , while watching the TDC mark. Keep revving until it stops advancing. Record the rpm. Now, keeping the rpm, at the number or higher, set your Power-Timing to 34*. I say 34 because at your pressure, it might be dangerous to run any more,as regards detonation.
At this point for now, all the other timings have to take a back seat. But at 34* at least you shouldn't be breaking stuff. And if your rough and poor running issues were due to detonation, that should now stop.
Step-2
Your idle-timing is now "fixed". Not fixed as in repaired, but fixed in position. It is what it is because it takes a backseat to Power-Timing. Whatever it is, it may not be right for your engine. @Mattax is really good at showing you different curves and how they play out.
The right Idle-Timing for your engine, at your cylinder pressure, will be between 12 and 18 (with an automatic). Do not compare your engine to anybody else's. Your engine will tell you what it wants if you let it.
To do that; the short story is; at idle your engine is idling on fuel that it is being pulled from the transfers together with what the engine can pull from the idle-discharge ports. Those two should be the only sources of idle-fuel. Furthermore, the ONLY source of air, should be what is coming in thru the primaries. All other throttles should be closed up tight but not sticking. All vacuum taps on the intake must be proved not to be leaking. And the intake manifold must also be proved leak-free. The only exception is the PCV valve, which must be plumbed to enter just beneath the primary throttle valves.
So, then,
you set the mixture screws to, in the center of their adjustment range. Then adjust the speed screw to give her what other fuel she needs, for a smooth idle. If the IDLE-timing is too much, the throttle will have been too far closed. So now with you tweaking the speed screw, the rpm will rise up and be too fast. The only way to slow it down, is to take timing out. And this is the correct thing to do.
However,
when you do this, you are simultaneously destroying your Power-Timing. This is where the FABO timing plate come in. You install it at whatever position gets you both numbers. Such as 14 at Idle/34 after 3000.
If you have an automatic trans, your engine does not much care about any timing between idle and stall. So let the engine tell you what it wants and just make her happy at idle. Do not force any more on her, it will just give you other problems.
Now, if your engine has a big cam in it, say [email protected] or more; you are gonna get into an unhappy place where the engine is asking for say 14*, but you just can't get her to smooth out, and the exhaust stinks so bad it makes your eyes water and hurt. If this happens to you, the engine is wanting some idle air bypass; that is air that enters below the throttle plates, like where the PCV valve enters. Or you can do what most of us do, drill tiny holes in the primary throttle valves. Either of these two methods, IMO, is acceptable.
Step-3
So now, having established the two basic points, of 14*@under 1000, and 34* after 3000rpm, we have to connect the dots as quickly as possible, yet not so quickly that the engine gets into detonation. This is handled by the springs in the Distributor (hereafter just "D").
At your pressure, you may have to delay the "all-in" timing to well after 3000. I'll guess 3600 .. So you are gonna need a tighter than usual advance spring set.
And, you will want a stable idle, so the timing can't be jumping around under say 1000rpm. So now you have two data points; 1000 and 3600. Go find out what yours is doing and how close it is. Maybe what you have is close enough.
Lets say it comes in exactly as above. Then your curve will be 14 to 34, at 1000 to 3600. By the math, that is 20* over 2600rpm so; 20/ (2600/100) =.77 degree per 100 rpm.
So now you can figure a few things from that. Firstly, say you have a 2400 rpm stall; your timing at 2400 should be 2400 less 1000, divided by 100 and multiplied by .77 equals 11degrees which you add to the 14 Idle-Timing, equals 25* of stall-timing. So now, if your engine doesn't detonate on that, then you can try to speed things up a bit. But if it does, then you have to slow it down. This is done with different springs. But if you have a 3000 stall, then at 3000rpm your timing will be;
(3000 less 1000/100) x .77 plus 14= 29.4...
and so on.
Eventually, you may find that my initial guess of 34* at 3600 was too conservative, and so you can change your timing-plate........ and start over. Or as your tuning skills improve, maybe you can run more Idle-Timing. If you change either of those, then you have to re-examine your springing. lol, ain't HotRodding grand.
Step-4
Ok now we can figure out your cruise timing.
Firstly we need to know what your Cruise-rpm is, so lets take it at 2400.
Previously we found that the timing at 2400 was 25*. Now, is the time to hook up the V-can and map it. Suppose at 2400, your can is able to bring in 9 degrees. Your Cruise-Timing then, will be 25+9=34 degrees.
But is that correct?
Here's how you figure out what your cruise timing should be; For this test, the rpm must be kept at Cruise-rpm/2400 in this example. And the V-can must be working.
So then rev it up to 2400, while simultaneously dialing in some advance. Don't even look at the timing marks. Just keep advancing it until the rpm no longer increases at 2400 with additional advance. Now, read the advance at 2400 with a light.
Suppose you got 53*. That is what she likes at 2400 in Neutral. She just told you so. Now take out 3* for load compensation, and end up with 50* as your target.
But, but, but we figured out mathematically that 34* was all you were able to get. So your 9* can has got to go.... Hang on; firstly, if it's a Mopar can with a hex shaped reservoir, it's adjustable. So go find a 5/32 hex-key (allen-wrench), remove the hose and stick your wrench in there to find the socket. Then crank it CW until it meets resistance. Do not force it past the resistance. Now it will advance as fast as it can, to as much as it can.
Next; there is a number on the arm, like 7 or 9, or something. This is the max number of degrees your can is able to advance, in distributor degrees so, you double it to read crank degrees. So a #9 is 18* crank.
On the arm, you will find two stops. When vacuum is applied, the stops hit the back of the can, and stop it from advancing any further. You can cut some material off the stops, until she hits about 22/24 degrees. But leave the stops on there to not tear your diaphragm. So now, say you get 22* out of your can.
Add that to the 25 mechanical, and you get 45* is the best you can do. If you are not looking for max fuel economy, just leave it. And if your engine does not overheat in traffic, just leave it. Those last 5 degrees you can think about later.

Ok so where are we?
Oh yeah
You have to get your timings at least close, before you start throwing fuel at it. ....... which you will have to do eventually.

But when you speak of the engine not wanting to rev past a particular rpm, no matter what the throttle setting is;
and the advance mechanism is responding,
and the strobing is consistent, then;
One of about three things is happening;
1) you have hit a rev-limiter, lol, or
2) you have a mechanical problem in the valve gear, or
3) your cam-timing is out to lunch.
4) or your exhaust is plugged, but with open-headers, obviously that one does not apply.

Lack of timing does not act this way.
Fueling does not usually act this way, until the fuel-bowl is close to empty.. then it stalls.

For purposes of tuning; disconnect the linkage from the outboard carbs and wire them shut.