Transmisson and Rear end oil change

[Mark]

I dropped the oil out of my HG transmission and rear end.  I refilled with the specified 2 gallons and then checked the level plug on the side of the transmission.  No oil in sight.  I even pulled the drain plug on the tranny and nothing came out.  Obviously, oil is not getting to the tranny .  My manual says both units are lubricated thru one source, the filler plug on the top left side of the rear end.  What am I doing wrong?

Thanks