in 01 the trucks with out trailer tow only had the lines to the radiator heat exchanger. On the tow pack trucks the lines went to the heat exchanger first, then the cooler, and back to the return. Yes, the trans temp has to be a certain temp before OD, lockup can occur.... hence the reason to run it through the radiator to aid in warming the fluid. believe the temp is around 80 degrees on my 47re before it will go into od.

on my 95, in the desert southwest, a also added another cooler on the drivers side (dodge Dakota cooler fit in the area off to the side of the radiator nicely). When we'd go to the cold in the winter I'd have to cover the third cooler as it would take miles of highway driving to get the temp up.