Slight miss in my 69 Z28

[PeteLeathersac]

Check and clean all connections including coil and battery also grounds, everywhere!
Try hot-wiring direct power to the coil also run it in the dark and look for jumping spark.
It may even be the Coil itself, they do goofy things sometimes although usually @ higher revs.
And distrib' shaft play can cause erratic gap too also act differently whether under load or not.
If you're still thinking vacuum leak, even though you've swapped the booster hose it may be best cork it off to test and discount booster itself as leaking too?
Keep trying and good luck!
[img]<<GRAEMLIN_URL>>/beers.gif[/img]
~ Pete