i check your profile and have to say You are old. was your first car a model t? did you walk to school uphill both ways, barefoot in the snow?

 

Mine has one as well. I also do not know what it is for either. I was just under there the other day doing an oil change.

 

It could very easily be a power-steering cooler. That actually makes more sense than anything at this point.

 

It is a P/S cooler. My 05 ram has one as well. I tried to install a trans cooler, but cannot find a good place to run the lines, without running them under the radiator support. Behind the engine won't do much good, and I don't want to cut any metal out of the way. Every place I tried to run the lines, they either get pinched, or they run too close to the ground, Parking curbs and such.