I am trying to use a filter instead of a transposer because its (supposed) to pull the max stack size (up to 64)... but its only pulling 1 at a time?

Am I forgetting basic RP functionality?

I have an item in the filter... but I don't want to set a specific number of items to pull.. I just want a stack at most...

Yeah, put in a full stack in the filter slot, because putting in a single item means it'll pull out a single item.