I'm at a loss and grabbing at straws...

Put a fuel pressure gauge in-line and use a length of hose to tape it to your windshield. Take it to a safe place and do some pulls and watch what the fuel pressure does at higher rpm.

It will either tell you there is an issue or eliminate the possibility

 

How about lifter preload? If too much it will kill rpm. Adjustable pushrods?

 

If its breaking up and missing that's not running out of fuel.....running out fuel just feels flat not missing or breaking up.

Breaking up is either valve float due to weak springs....or as mentioned as the rpms increase the amount of time for lifters to bleed off reduces and ifvthe valve get hung over.....it can cause that.

But it sounds like valve float. Not sure how much lift your cam has......I ran ta stafe1 plus spring with several cams up to low .570 lift with no issues or float to 6500 rpm, and are basiclly drop in on iron heads.

Checking fuel pressure under load won't hurt to help rule one thing out. But have fuel pressure doesn't mean the motor isn't running out of fuel.......I went to low in jets b4......had plenty of fuel pressure....but car would nose over and go flat b4 the 660ft......but it didn't break up and miss.......just fell flat. I've had bad incorrect springs installed b4.....and it would go nuts like that every time it got near 5000. Popping and all.....let off a touch it would go away,

 

Have you pulled the spark plugs and see if they are fouled ? Just went through this on a car ended up being a bad MSD cap that looked fine ..

 

I also just had to fight through a bad msd cap. But a new msd distributor in a boat with a fresh motor.....it would should spark on all cylinders.....I could put my timing light in each and rear the same rpm, but within a mile or 2 on the water #2 would carbon sooty black.......tried everything else wires etc.....put a new 50 dollar cap on and it went away.

The odd thing was with a new plug in that hole....it would run right as rain....full rpm full mph for those 2 miles the just fall flat......but never popped and banged or misfires and would still read rpm on the timing light........very very strange

 

Here's how I did it with stock fuel line and the Summit gauge.

 

I would check fuel pressure although I'd expect the stage 1 pump to keep up at that rpm. You won't want to hear this but a couple of flat lobes will cause your symptoms all day. Before you start throwing parts at it I'd pull the valve covers and verify you haven't lost the cam. If that checks out I would suspect the points elimination kit.

The 10 year old valve springs are nothing to worry about. The 413 cam is a bit rowdy but is not a brutal race cam by any means.

 

Fuel tank,....been there done this,....the fuel is moving around and with a mechanical pump especially thus can't happen,....some of the new tanks are baffled,....that's what you want also,..an in tank submerged pump will solve any delivery issues,....the regulator isn't cheap but it solves the problem

 

I had issue where new cheap rubber fuel hose by the tank was soft and would suck closed in warm weather. Thought it was vapor lock. In cool weather it didn't do it cuz hose stayed more rigid.....Replaced with marine 3/8 hose and fixed it.