I'd get with a trainer and up the firmness of your handling. If I were to choose the trainer, it would be someone that does IPO or sport, one who understands the GSD, and not a behaviorist.
Your dog is mature, showing that he is in control when it should be you instead. Find a club and go see if there is a good handler willing to help you work on this(not train in the sport, but show you how to work w/ your dog)
I'd also up the NILIF
and let him know that you have everything under control so he doesn't have to be in charge.
The two week shutdown
may help as well.