tow
Usually the "towing package" from the factory consists of one or more of the following:
Lower gearing (3.73, 4.10)
Super engine cooling
Higher load rear springs
Larger rims, tires
Class III hitch
Wire harness plugin and/or complete harness
Thing thing about factory "packages" is many of these items, like the larger wheels/tires, or the gearing is available without the package, or as part of another package.
I have the "towing package" on my '93 but the only thing that seems any different to me from a stocker is the super engine cooling- the springs, rims/tires and everything else is the same as a stock-o sport. I don't even have real low gears or a hitch- and the harness had to be hard-wired in!
I think as long as you have the gearing, you could go out and equip your X with aftermarket accessories for towing and it would be alot better than factory. Tranny coolers, heavy duty radiators, hitches, and even plug-in harnesses are available for just about every truck on the market. You can get add-a-leafs or new springs if you need heavy hauling capabilities. I think about $500-600 would get you everything you need- plus labor if you dont do the work.
I doubt this makes a huge difference in the resale value of an Explorer, so if you find one with a towing package already on thats cool- but you may also consider just buying something that has never even seen any heavy duty use let alone towing- might be in better condition, and you can just add the aftermarket towing parts you need.