I chased this issue for a frustrating amount of time with my motor running with a rebuilt Holley. I was convinced the intake must be leaking. The idle would wander and increase 300-400rpm after driving.Tried spraying choke cleaner and starting fluid around the carb and intake with no results.
TXDart was kind enough to put his smoke machine on the crankcase, and when we covered the bowls smoke started shooting out around the throttle shaft. Swapped on a different carb and now it idles and runs great!
Not sure what the history is on the carbs you have run on it, but either way a smoke machine test might be worth paying for.
https://youtu.be/E68FD_mJ8Ew