Tim Brown was able to make his moves at close to top speed and then apparently just keep on going. In reality, he had exactly what you said in your post. He would slow down just a tad right at the perfect time, juke just a tiny bit, and then boom within 1 step he was at top speed again and the guy was grasping at air where he thought he was originally headed.
Rocket was similar, but as a high school RB, in many cases he simply ran though the tackle at top speed and just kept going.
GAIII -- right now -- has to slow down way too much to make his move, so he can't get back to top speed fast enough to essentially do what Brown and Rocket did on a more consistent basis even though he is about as fast as they were. I still hold hope he will learn it to a greater extent and then he is going to start to really play at a totally different level.