Great thread
I have been chasing a similar issue with the Barracuda engine .
Plugs look lean but eyes say rich ! AFR is all over the place
Run both a Slayer Holley 750 VS and now a new 650 AVS-2 ... engine blubbers a bit up to 2000 rpm... recurved the dizzy 100 times ...changed rods and jets lord knows how many times !
Starting to think the Cam is crap grind.
Got a ton of cylinder pressure (170ish )
11” vacuum at idle , 15-16 @ cruise .
Mileage sucks.