Well so far what i have come across at a few points is!
When i come to an incline on a path,hill,road my guy will stop the fast sprint and either fast walk or just walk depending. i understand thats kinda normal but when your being chased by an epic zombie who's pase seems unaffected by the incline its rather annoying.

long & short of it.. zombies arent affected by inclines. cant run away if a zombie can run up a hill faster than you.