Get rid of the tanks first
Move fast as soon as the mission starts and make sure you get rid of the tanks before they reach the target truck. Wait for the tanks on the road then destroy them.
Wait for the truck on the road
Wait for the truck on the road. Use the D-walker to move fast in order to be able to intercept the path of the truck.
Encounter the truck in an empty area
Make sure you encounter the truck in an empty area where there is no enemy presence.
Shoot the Driver from a distance
As soon as the truck appears shoot the driver. If you did it right he will either stop the truck and get down or fall dead right away.
Hide fast before they see you
After the truck stops you have few seconds to hide before you get spotted. This is why you should attack the driver from a place that allows you to hide.
The skulls will arrive at your place
The skulls are programmed to move towards you even when they don’t see you. Probably they try to go to the place where the gunfire occurred. (See How to detonate C4 – Phantom Pain (Metal Gear Solid V))
Circle around the truck
Circle around the Truck , from a big distance, while crawling in order to be out of the eye of sight of the skulls. If done right the Skulls won’t notice you.
Move towards the truck
Move towards the truck. Make sure you are not seen. As soon as you reach the door get inside.
Move away from the skulls
Quickly move away from the skulls. Go as far as you can. Also make sure you avoid area’s with enemy presence. When you are safe open the map and see where you need to go to exit the hot zone. (See Why Playstation 4 is good?)
Warchief Hunt - Middle-Earth: Shadow of Mordor Wiki Guide | Shadow of mordor - How to kill warchiefs