Here is my process:
Cook it (wrap in foil at the end to capture juices)
Let it cool and refrigerate it overnight
Slice it the next day (while cold)
I usually freeze it, but it sounds like you won't need to
Reheat in pot of simmering water.
I refrigerate it before I slice it so that the fat and juices congeal. This way I can put a spoonful in each bag and it won't get sucked out when I vacuum seal the bag. Moisture retention is never an issue for me.