My truck had a transmission cooler from the factory, but it had small leaks.  I went to Pepboys and bought a Hayden transmission cooler, which was about twice the size of the original.  After I took out all the brackets that held the old one, and the new cooler fit nicely with zip ties.  It sits in the same location right behind the grill, but actually takes up less space because the old brackets have been removed.

Next time I have that grill off I'll take some better pics