You need to check the vaccuum lines at the pump. Do a vaccuum test with a mighty vac hand held vaccuum pump. If it does not hold vaccuum then you have a leak on that line.
Your a/c problem can be caused by the hubs. But you need to test the system before you start tearing things apart.
Sometimes the hubs will make a noise and sometimes they won't. What you can do is put the trans in neutral. Jack up the truck block the rear tires so the truck. Then turn the front tires by hand. Watch the front driveshaft see if it turns.
I forgot the vaccuum pump is located on the passenger side of the engine compartment behind the battery on the passenger side wheel well.