I've had gsd's for years, and one thing I can say about them, is they are not stupid dogs. They know what works for them, predictable or not, they can anticipate whats coming pretty darn well.
Another thing is, if your not consistent every single time in whatever your doing, some will walk all over you and push things to the limit.
It doesn't take them long for example, to figure out,,if I go to the window and bark , my owner is going to call me, and give me a treat..SO to get that treat, I'm going to go to the window and bark !
In one post I saw you write, that when your roomate wasn't there, you'd let him bark and whine,,UNEXCEPTABLE,,he doesn't give a fig whether your roomates there or not, you let him bark or whatever, he's gotten away with it.
I also saw you post he lays around on your bed for 10 hours a day..TO MUCH DOWN TIME..
I'd be running this dog ragged, amp up his exercise especially at night. Take him hiking, take him swimming, take him to CLASS, a walk is not sufficient. Start working on a good LEAVE IT, and incorporate that into EVERYTHING.
He knows what works for him. He doesn't know "how" to behave because it's not been consistent..If you can't figure it out, get some professional help..
Key is to be consistent, FIRM and FAIR.