Slow starting1999 3500 van

When the van has sat for a couple of days it does not go right away when I put it in drive. Once it gets fully engaged everything is fine and no problems when it only sits up to a day or so. Is this due to the the torque converter losing all its fluid and not getting re-filled with fluid right away? Is that normal?

I don't think it is normal I would change the fluid and filter Its a sign but keeping transmission fluid changed annually and full it should last some more time. If you do it yourself it isn't that costly.
The big thing is the fluid isn't burnt and the pan isn't full of metal.