Before you take your decision on which way to extract the truck (which is required to end this mission), you need to know the BIG handicap to the completion. After you approach the truck, at the distance of around 20 meters, a cutscene starts. Around the truck, there appear the Skulls, i.e. very strong and very agile zombies that you have already dealt with in previous missions. After the Skulls appear, it is best to finish the truck extraction process, although you can also start fighting the enemies. (this is a secondary objective of the mission, which has been described on the next page of this walkthrough).
It is best to extract the truck while it is still parked at Nova Braga Airport. If you have the CARGO 2 upgrade, you simply need to run up to it and, while ignoring the Skulls, attach the balloon. After you succeed, leave the airport (preferably, across the gate mentioned on the previous page). Hop onto the horse and start escaping from the Skulls. The mission ends at the point of leaving the area of operation and you should easily get the S rank.
If you do not have the CARGO 2 upgrade, the only way to complete the mission is to drive the truck outside of the map. Of course, you can steal the truck when it is still at the airport. In such a situation, try to neutralize the enemies around beforehand and do everything still before the convoy arrives. Right after you get into the truck, leave the airport as quickly as possible and continue driving. Remain on the main road to prevent slowing down too much and prevent the Skulls from landing successful attacks. The mission ends in a success if you leave the mission area before the truck is destroyed.
If you did not reach the airport on time, the truck joins the convoy and heads towards Kiziba Camp. It is not a good idea to attack the convoy along its route, because you would have to destroy quickly two APCs (e.g. using the rocket launcher) and stop the escaping truck itself (by neutralizing the driver). Instead, it is better to wait for the convoy to reach its destination and only then, sneak up to the truck and fulton it, or get into the cab.