How much RPM drop from park to drive with stock type 340 convertor

AJ/FormS said
The idle drop is caused by one major thing; and maybe two other minor things.
1) transfer slot sync, and
2) transfer slot sync, and
3) probably you guessed it, the transfer slot sync.

What is 'transfer slot sync' ?

Is it the 'off idle' circuit - idle air bleed ?
How does drilling holes in the primary throttle plates work ?