How do I test it? I've searched many forums but I can't find a definite answer. And where do I hook up the voltimeter? If there's an explanation somewhere I would appreciate a link thanks

 

Easiest way to test is:

Remove from truck, leave electrical hooked up.
Hook up a vacuum source, with a gauge......
Suck some vacuum, compare what the gauge says, to the the PCM thinks. If there is too much margin, replace it.