Taken from a port right under the throttle body I can check for vacuum tomorrow under that throttle load and see. If I’m remembering correctly I think it’s close to 0. Will update with the number the Holley puts out with the internal 1 bar mapAbsolutely!! I bet that body wasnt even flowing 750CFM at that setting. When the blades are cocked over like that, the disruption in the laminar flows are giant. You've probably got some power on the table too. It'd be worth testing a 1 and 2" spacer beneath the TB. @5700rpm, the engine (357ci) is pulling roughly 500-520cfm @ 85% efficiency, and I'd gotta think you're better than that. As flat as that graph is, it's running out of air, which is why I was thinking it wanted more over lap or something.
Did you guys have a vacuum sensor connected?
At full throttle, top of the RPM range, you only want about .8-1" of vacuum. With that throttle position, I bet you were closer to 5-7" of vacuum.