The Buick's max rating is only 3500 pounds and only with the "factory towing package" whatever that consists of.
That capacity will pull a 2500 pound trailer nicely and allow passengers and camping gear inside the tow vehicle without exceeding 3500 pounds. 3500 is the total of the trailer AND internal load in the tow vehicle.
Vehicles like the Explorer, TrailBlazer, etc. are sold as station wagons, not tow vehicles and unless they have factory tow packages are rated about 3500 pounds too -- don't make any assumptions! Small so-called SUVs like the Escape are only rated at 2000 pounds but go to 3500 with the factory tow package (which also includes the receiver!).
You don't need add-on transmission radiators if the tow rating is already adequate, but they're often the only difference in tow ratings.
As an example the standard tow rating of my Expedition is 6000 pounds. The factory HD tow package adds wiring (something ya need!), a larger engine radiator, and a larger transmission radiator. That's it. Mas towing capacity jumps to 9000 pounds. My Explorer jumped from 3500 to 5500 pounds with the wiring and larger transmission radiator.
HD tow packages rarely have any negative effects on things like fuel economy. Always order one with any new vehicle. Only $300 or so when new.
'06 Roo 23SS behind an
'07 Expedition out of Cleveland Rockwood Roo 23SS