As far as I know all tow vehicles, at the very least, have a built-in tranny cooler, but as Dan Burwinkle points out they are barely functional, certainly not adequate for towing. And, no, the ones with a towing package, while they have perhaps a larger built-in unit (I think they also have a larger radiator--my
Suburban does) it is not adequate for the kind of towing we do. I have always used the largest Hayden cooler (although I believe there is another of quality--perhaps Tekonsha?) It should not be hung on the radiator, but mounted in front of it to allow more free flow of air.  Furthermore, the hot oil from the engine should go to this auxilliary cooler first, and then return to the built in cooler and then back to the engine. Reason: In winter the auxilliary may cool the oil too much, and whether winter or summer,
running it back through the built-in cooler ensures that the tranny oil is maintained at some approach to a standard temperature.

Reference the round can at the side of the radiator. It is part of the emissions control. Persons who notice a continuous smell of gasoline around their tow vehicle, may have been overfilling their tank, thereby soaking the filtering material in this can with raw gasoline. ( Hint: when filling your tank, let the pump cut it off every time and you won't have this problem.) Check your owner's manual, I believe this filter is to be replaced at some extended period.

How do I know when I am no mechanic?
1. I only patronize well qualified shops
2. I ask questions because I am just naturally curious about everything!

Happy motoring, keep it cool and clean!

Donald