Are you on PC? If yes it migh be not "powerfull" enough or your setting are to high for this to work smoothly. I've occasionaly played on my pretty poor laptop and had exactly the same issue - people around me were walking faster than I was running. Try to decrease the resolution / change to display mode to see if that affect the walking / running speed. Also be sure that you don't have the "slow walk" on by accident (/ on num pad). That's indicated by the "walk" icon in the top bar with time and connection speed etc.