Slant six 4bbl

I have a 67 slant six 4bbl (edelbrock avs 1801) runs good and idles ok , and I say ok because once in a while it does this little hiccup when I’m at a red light or stop sign but as soon as I hit the gas it goes away and runs good and strong . Also when I’m going at a good speed 35mph and up and I come to a sudden hard stop the engine “gags” or “hiccups” but 90% of the time it recovers and starts idleing fine.at first I thought it was a heat soak problem so I slapped a phenolic gasket under it ,carb stays cool but still gags at idle sometimes. Carb is stock internally ,timing is at 10* btdc ,idle in gear is at about 600-700rpm,manual steering and brakes. The only thing I can think of is some kind of vacuum leak or float level somehow came out of calibration. Anyone have any ideas or has had similar problems with their slant 4bbl?