what size transmission fluid hose do I need for the trans cooler? 3/8 or 11/32 inner diameter?

 

It comes with the tranny cooler.

 

I think 3/8" sounds right. You can go to the autoshop, and ask them for transmission fluid hose...I think it comes in a standard size. Get some 3/4" hose (called heater hose) also when doing the install to insulate portions of the tranny hose from rubbing against the ziptie connectors.