What is this part of the transmission called?

I own a 2002 Ford Explorer v8 4.6L 4x4, anyway i'm not certain on what the part of the transmission is called, it connects to the two drive shafts one in the front and another located in the back, I'm trying to drain the fluids but also not exactly certain what fluid I should consider using, the normal transmission fluid maybe? Because it makes an odd humming sound when I slow down and the transmission itself slips every now and then, anyone know what the assembly is called? Thanks!