I can normally run about 4 or 5 steps but when I try to do it on certain maps I kick my leg straight out instead of pulling it behind me.
e.g. On classic I can run over to Uke and kick him but on parkour_city_a, I trip because I kick my leg out instead.

The thing with running in mods is that youre usually ontop of an object, which lets your tori slide a bit with every step, so the running style you are used from classic doesnt work there.

means, running on an object is quite a bit harder, try around to contract/extend your ankles and try to keep your centre point a little higher makes it a bit easier aswell. also contracting your knee, so the leg is higher and you dont trip over your foot is another way you could try to run.

all of this may require you to work with lower turn frames than 10 (if you aren't already) so i recommend the use of shift + space which always lets you pass 1 frame.

Most of the time it has to do with friction properties, as well as the gravity. I'd check to see if those are issues as well, but be safe and take it either one frame at a time or 5 frames at a time to really make things look fluid.