I'd suspect corrosion inside of the terminal ends, where it's swaged to the wire. Longstanding terminal corrosion can creep up into the wire, and make a poor connection there as well. If you do need new terminal ends, skip the clamp-down style ones. Only soldered, or mechanically swaged, will work as well as OEM.
Try wiggling the battery wires (and double check they aren't loose), and see if that helps. If it does, you most likely need new ends.
2000 E450 dually V10 wagon