Running the tranny lines thru the radiator actually cools the fluid even more. A transmission can hot as 250 degrees under normal driving, running the lines thru the radiator first. Even if the engine coolant is at 190 to 200 it is still cooling the trans fluid, then run your lines to the trans cooler for more cooling before running it back to the trans. This will give you the most cooling for your trans, There is different size coolers, make sure to match up the one for your application.:SNSign: