Only SOME rads have the trans cooler integrated into the bottom portion of the rad. IF you have one…and I dont think you do unless you have an auto trans…and I doubt that. Sometimes they will install only one style of radiator…(like todays aftermarket) and this would be the auto trans style rad…you can use this style in an auto obviously but also in a manual…as it wont harm anything to not use the cooler lines if you dont have the auto…I have run my engine oil into one of these radiators one time just to rig up an oil cooler of sorts…not a great idea and didnt do much cooling but it was there and I wanted to say I did it…I was 18 at the time…so I was goofing around.
Now on your truck…I really doubt you have an auto…am I wrong in this assumption? If I am not then your trans lines will enter the rad near the bottom or on one side or the other…you will see a bung on the rad…hard to miss…but if this ever sprung a leak internally it would surely puke the oil into the coolant.