It's possible you are misremembering. He's never been a guy with a high gear.
He runs fluidly, has good lateral movement, and has amazing vision, but he's not a fast RB.
Watch his first TD as a cougar, against Arkansas last year. He finds the hole and makes a great cut up field, which got him into the 2nd level beyond the defense. But the DB pretty easily caught up to him and nearly got him down before crossing the goal line.