newbe with trans cooler question

02 d-max/Allison I am installing a haden high flow 3/4 cooler, what do you think about eliminating the radiator from the trans cooling system,& does anyone know which line is supply / return . I pull a 15,000 toy hauler amongst other heavy things and the trans gets hot 7000mi on last trans service and the fluid is very dark does not smell like clutch material but obviously got to hot, trans shifts fine but need to get that cooler in i would appreciate your opinions thanks