Whenever I add an external cooler I always totally bypass the radiator porting....I add plugs to the radiator ports to prevent any water loss if the radiator cooler ever dies....
Most engine water temps nowadays are over 210....which can reduce the efficiency of the plate air based coolers....the trans fluid could be matching the water temp then cooling down a bit when run thru the plate coolers....
Make sure the coolers have sufficient air flow thru them....and are not stacked one behind the other....
