YES, you do have the Diode in your trans. If the trans has been rebuilt before you bought the truck, that part has been replaced. From the start of the '01 build till March of '01 the Diode will be in all Diesel 4r100 trans.

As far as changing the fluid in the trans, follow these instructions from Mark K. Changing ATF Fluid in a E4OD and 4R100 transmission .: Articles