Is your GSD your only dog?
Dion used to do that before we adopted Zac. He would take all day to eat his food (if he could... if not, he'll take 15minutes, which was our time limit for him).
As you described, he'll take a mouthful and go elsewhere to eat it at a leisurely pace (usually just 5 steps away), and then come back for more.
However, ever since we got Zac he became more guarded with his food bowl and wouldn't leave it alone.