8.5. After a turnover, and after the pull, the team that has gained possession of the disc must continue play without delay.
8.5.1. An offensive player must move at walking pace or faster to directly retrieve the disc and establish a pivot.
Where does it say that you can't change pace? If I am jogging I am technically faster than walking pace, hence I am moving "faster" and so within the "faster" category I can choose to jog or run or both.