Re: Factory tow pkg
The following items can be added "aftermarket" if you wish.
-7 and 4 Pin Wiring Harness
-Class IV Receiver Hitch
The WK2s have the wiring harness installed for most (if not all) trim levels, just have to get it activated at the dealership once you throw on the 7/4 pin plug.
The full size spare (vs half-sized) comes with the tow package too (as well as other packages), but has nothing to really do with towing. The rear load leveling suspension you already know about.
The part that cannot be done aftermarket without a great deal of expense is the "heavy duty engine cooling", as you already suspected. I believe there is an additional oil cooler, and a more powerful, more variable engine fan.
2014 Jeep Grand Cherokee Limited 4x4
5.7L Hemi V8, Luxury II Package, Navigation
Hemifever Tuned, Billet Catch Can, 265/60R18 Hankook Dynapro ATMs