Heres the low-down on cooler line fitting thread sizes.....
97-Most 99s:
Cooler FEED fitting (points straigth down) 1/4-18 NPSF, NO CHECKBALL
Cooler RETURN fitting ( Horizontal-points towards front of car) 1/4-18 NPSF
Some 99s, all 00-early 04s:
Cooler FEED fitting (points straigth down) 3/8-18 NPSF, HAS CHECKBALL
Cooler RETURN fitting ( Horizontal-points towards front of car) 1/4-18 NPSF
Early 04 to current:
Cooler FEED fitting (points straigth down) 9/16-18 UNF, NO CHECKBALL
Cooler RETURN fitting (Horizontal-points towards front of car) 9/16-18 UNF
I think it feeds the top. that way if you are low on fluid..it falls to the bottom and you don't run dry
The fitting on the transmission that points straight down towards the ground is the feed fitting that sends fluid to the radiator transmission cooler, which should be going to the bottom fitting on the radiator.
The fitting on the transmission case that is parallel with the lower pan and points straight forward is the return fitting from the radiator and should be connected to the line going to the top fitting on the radiator.