Radiator and Transmission cooler system

[collega]

Hello, everybody!
I read from internet that some guys after 100,000 miles sometimes had some problems with their radiators when gaskets not good any more and coolant could be mixed together with transmission fluid and pollute transmission that leads to failure and broken it. For this purpose some guys try to by-pass and put trans cooler outside of big main radiator to prevent this costly damage and repair. I check my 2003 H2 and found out that outside of big main radiator there are two smaller coolers- radiators in front of big one. One of them is smaller than main radiator and another one is even smaller that other ones. So my question is: Is it original assembly in this way or may be previous owner of my truck did that change and put outside of main radiator transmission cooler and oil engine cooler to prevent costly damage? My mileage is around 140,000 km so I should keep my eye on those kind of things. Is anybody have any idea and knowledge about this kind of job?
Thank You.