The self leveling rear suspension comes with the 3rd row seating option. I tow my boat which is right around the 6k lb mark with no issues. Plenty of power, and good braking. No trailer sway either.
You really should get the car reprogrammed if you have the OEM wiring harness installed. You get an additional zoom mode on the camera for lining up the hitch to the trailer, and you get stability control to prevent trailer sway.
Here is how level the back of my X5 is while towing
