Battery looses Charge - I’m at a loss

Have you checked out the glove box lamp? I could not see mine was "on" through the crack in the joint of the door, but it was.......pulled the bulb, problem solved. Have you actually disconnected the radio memory, or the radio completely? Also some of those whether "in the radio" or an auxiliary box, have the transistors connected to power at all times. They are supposed to "cut off" when the radio is off, but they can "leak"--just like an alternator diode.

Just for info, the alternator could have been easily checked........by you. Hook a test lamp in series with battery ground and unhook the alternator output wire

As someone mentioned, you seem to be on the right track. Test lamp/ current mode meter is your friend, you seem to already know the fuse

Search online for a shop manual for your Dakota, I've downloaded a few here and there. Links come and go, you have to spend some time