2001 Ford Mustang V6 Auto Waterpump Issue

My mustang recently was having issues this fall where it was making a chirpping kind of noise, so I took it into to the dealership and told me it was the water pump and a tensioner needed to be replaced, so I had that work done. It only took like 3 trips for them to figure it out, non the less I was not to happy with the mechanics after all that crap. So when I went home up north over break the engine cut out randomly so I brought it to my local mechanic who looked at ran some tests and told me that it was the waterpump. So long story short I brought it back to the dealership told them the waterpump was messed up and then they call me today say the water pump is fine and is a cam issue with lubrication and that I need to replace the cam now. At which point I told them not to do anything because I don't trust them and after getting off the phone with my local mechanic from home he is 99% sure its the waterpump. So long story short what should I do, take it to another ford dealership since the waterpump is under warranty or take it somewhere else local?

mike - Before I did anything, I'd ask that hometown mechanic to explain how a bad water pump causes the engine to cut out randomly....