Vscript to make trigger_multiple act as hill climbing trigger. That means moving up slows player down to walking speed but moving in different direction will keep his normal speed. 

Make trigger_multiple representing the section where player should be slowed down when moving up the hill

Add info_target about 100 units above the top of the hill. This is a point towards which player needs to walk to be slowed down. Give it some name.

In the trigger_multiple turn off smartedit and add key target with value being the name of your info_target

Set Entity Scripts key to trigger_hill_climb.
trigger_hill_climb.nut must be present in scripts/vscripts folder when you run the map (the link to it is at top of the page if missed)