Part identification help

[Mike GMC]

I was looking at the accessory drives on the front of the engine and there is one item I can't identify.  It has its own small belt and is located driver's side down low.  I would normally think power steering pump, but this one is electric steering.  What is that thing?  External oil pump, air pump, vacuum pump...?  It's driving me nuts trying to figure it out.  Thanks.

[Mike GMC]

After more digging on Rockauto, it appears to be the vacuum pump.  Actually has a stretchy, self tensioning belt.  I was wondering why I couldn't see a tensioner.