I am curious if anyone knows whether a factory transmission cooler was an option on the 2003 1/2 tons. It was on my list to install a cooler and upon inspection, there seems to be one already there. It is pretty small, maybe 9 or 10 inches wide and 6 or 7 tall. Trans line runs into this cooler, out, then into the main radiator and out back to the tranny. Was this likely an aftermarket add on or perhaps part of a factory tow package?

 

It's the factory cooler, part of the towing package. Always seemed sufficient for my needs. I have an HD cluster in my '01 half ton Burb, so I have a trans temp gauge. Factory cooler keeps the trans about 100° over ambient, even when towing heavy loads. Never felt a need for a monster aftermarket cooler. Trans has 205k miles, and still shifts perfectly. YMMV

 

Not completely sure about it, but...
I think there were very few that didn't have the cooler. Definitely all the Off Road/Towing rides did.

Just in case you didn't know...
Fluid went to the Cooler first,
Then to the Radiator Capsule to assure a quick warm up,
And, then to bring the temp down more, IF the cooler didn't.
Most Fluid Mfgrs want their stuff to operate at 200* or below.
Since most of our rides operate at 185*, that works most times.

However...
IF your tranny/engine is running too high, you can purchase a separate Valve assy, which re-routes the Fluid directly back to the Tranny when the temp gets to high, and a Electric Fan is placed on the Cooler. Both are temp controlled. This takes the heat load of the Tranny off of the Cooling System, so both are more able to handle hot places. Larger cooler assys are also available.