Does your radiator have a trans cooler in the bottom tank?
If it does, can fluid flow through it?
If it does not, a radiator shop can add one.
If you don't want to add one to the radiator you could move yours to Infront of the radiator so it stands a chance to get some air movement
Side note... A fluid to fluid heat exchanger is much more efficient than a fluid to air cooler. That 1.25 (ish) diameter cooler in the bottom of the rad can cool the trans where as a finned external only might not be able to under many situations.
