You can get a flat spot with the Edelbrocks when making an abrupt transition from primaries to secondaries opening.
Abrupt meaning tromping on the throttle as vs rolling it smoothly in.

Running at a higher altitude than you usually do can make the flat spot worse.

It is a flat spot though and it doesn't take long for fuel to start flowing in the secondary circuits and it's more of a bother than a giant pain in the backside.

Many of the Edelbrocks come stock with the orange metering rod spring.
Changing to a pink spring cured the stumble in my 750 Edelbrock.

It helped as well that I jetted the carb - jets and metering rods - leaner for the altitude I'd moved to.
3300' vs 350'.

It does sound like your engine is simply running out of gas and for that reason I'd make a point to check the fuel pressure under load.

Make sure as well you don't have a kinked fuel line.
Rubber and hard line....