Transmission Cooling Lines

Hello,
I have a 1994 RAM 2500 5.9L, I was under it yesterday and noticed that the Transmission Cooling Lines are corroded and starting to leak. Does anyone know if I have to drain all of my radiator fluid to replace these lines or is there a separate radiator for the transmission? I cant really see where the lines go once they go behind the radiator.
Also, I see one of the lines has a sensor plugged into it, what is this sensor reading? I dont have a temp gauge in my truck for just my transmission.

Just as a side note, these lines arent cheap! Has anyone successfully replaced these with homemade jobbers rather than the OEM metal tubing with rubber ends?

Thanks in advance!
Author: Whitemts