This is my take on figuring tow ratings.
2009 1500 Suburban specs:
Gross Vehicle Weight Rating is 7200#
Curb weight of Vehicle is 5607#
Cargo capacity is 1593# (people weight, pets, full tank of gas, any additional gear and TRAILER TONGUE WEIGHT.
So if you are close or at gross vehicle weight rating: 11500 - 7200 = 4300# tow rating W/O H/D cooling
14000 - 7200 = 6800# tow rating with HD cooling.
Your tow ratings will vary some depending on cargo weight and the tow rating is a loaded trailer (water, propane and stuff).. Don't want to exceed gross vehicle and/or combined gross vehicle weight ratings..