By the size of the cooler.
This is the oem, compared to the mishimoto cooler we sell, which is about the same size(just a few more rows) as a oem 6.0 cooler.

 

The cooler is in between the AC Condenser and the Radiator near the bottom. As @eric@cncfab said, stock one is small - 9-rows, if I remember right.

 

you sure about that?


you sure about that?
on my Excursion, the ATF cooler is in front of every thing, immediately behind the Winch.

 

Very sure. I replaced my 9-row cooler with a 6.0L cooler. If you look @ your first picture, you'll see the bottom of the trans cooler showing under the AC condenser. That small cooler in front is for the power steering. Follow the lines.