When running around the map i've noticed on every occasion i'm presented with an up hill incline i must walk up it unless i strafe up the hill on a certain angle.
Zombies however can run up the hill without losing speed. This is very annoying as if you are in a hilly area and have zombies coming for you essentially you are done for unless you turn and fight. prehaps running up hill should make you slower but walking pace is too slow. Also if like me you want to get to places "As the crow flies" this again proves to be a huge problem. as it would be faster taking the roads due to this issue.