Oldgunny,
Even though you have your autosave set for 5 minutes, AutoCAD saves based on event triggers, in other words, you must be performing some sort of function (command operation; line, circle, etc.) in your drawing for the autosave function to "kick-off", it is not strictly a timed event. So, if you don't perform any AutoCAD functions for 6 minutes, the autosave function doesn't kick-off, then once you begin working, the clock starts again. If however you are working in your drawing, and not saving, you should see AutoCAD display messages stating it is performing an autosave (if the file is small enough and your computer powerful enough, this may go by so quickly you can't see it). If you are judicious (obsessive?) about saving, and do so before your alloted 5 minutes, say every 2 minutes or so, normally the autosave clock is reset each time you perform a save and that may account for why it is saving at odd times. Finally, not every drawing event in AutoCAD triggers an autosave event, (it seems to me there is a list somewhere of which events trigger an autosave but I can't remember where or when I saw this), it is possible the commands you are usint do not trigger an autosave.
HTH
Todd