are you sure you understand what leash pressure is? IF you do and your dog knows leash pressure and your dog is getting in front a slight tug and stopping should make him back up to where you want. then move again. rinse and repeat. german shepherds are smart; if you are clear and consistent he'll understand what gets him the reward aka he gets to keep moving forward on his walk. if he isnt in the position you want then stop walking. only reward good behavior just like every other dog command.
teach him what the heel position is. its a command just like sit. if i say heel my dog runs to my left leg. again they are smart. a 2 yr old should know the command in 10 minutes if you are clear and the dog understands what you are wanting.
I know it's me, I just don't know what I'm doing I guess. He knows the heel position, all I have to do is tap my hip and he comes and sits right against my leg. When we are walking if I stop, like you mention, he jumps right back into position. But then it's right back out front as soon as we start walking. If I hold a treat, or ball, we walks perfectly, but then you reward him and it's right back out front again.
I do feel like we are so close, I just think I'm missing the correct way to communicate to him what I want I guess. I think a little bit of the issue is we walk in the same places, so he knows where to go, and also knows his favorite places along the way, like the park where he can run.