As your hubs do not have vacuum supplied at all times most likely they are not the source of your problem. As for the components you are asking about, one is the vacuum pump for your diesel and the other one is the vacuum control module to your hubs. You need to fire up the pickup and see if the pump is running and pulling a vacuum. Most likely problem is a broken line from the pump to the system or a bad vacuum can, but it could be that the pump has failed. Good Luck