One possibility I haven't seen mentioned is whether the carb base might be warped. That will for sure cause a vacuum leak. Possible causes include overtightening the carb to the intake (100 inch pounds max), especially with a thick gasket.
I checked the carb with a straight edge. Everything appeared to be normal. I'm going to have more time to look into everything this week. I'm probably going to tear the carb apart and rebuild it.