I can't say for sure what exactly Ford means when they say an Explorer has a towing package.
I'm pretty sure that tranny coolers are standard on all 2nd Gen Explorers.
Because we all know how sucky Ford auto trannys have become. That even with a stock tranny cooler many transmission won't make it to over 100K miles. The darn things should come with 3 tranny coolers stock! I've added a 2nd additional B&M 19GVW rated tranny cooler to my Limited and still can't believe some of the temperatures my tranny oil will hit during normal driving without a load. And it still isn't summer yet!
I'm pretty sure that for the Explorer, the towing package is just the 4 wire trailer plug at the rear bumper. Both my Explorers came with them. BTW, the Sport Trac also had two untapped wires hanging down near the bumper. One labeled "power", the other "ground".
On the bigger Ford's(F150s, F250, Expeditions, Excursions, etc.) I believe the towing package includes a wiring harness up under the dash making it easier to plug in an electric trailer brake controller. I know my Limited did not have such a harness and I had to tap in to wires myself to install my electric trailer brake controller.