360 dies at idle, but not when in gear ??? Huh?

Idle mixture set properly? In gear the engine pulls less vacuum thus less air/fuel (yes both) through the idle circuit compared to in park with no load without the converter engaged. Might be too rich at idle? What are the mixture screws set at?

Could also be some kind of vacuum leak that only shows up when the vacuum is higher in park and gets "bigger" when the carb warms up from engine heat.