We also have the air suspension which keep the rig level. Does well on flat highway, but engine struggles to maintain highway speeds steeper Interstate grades. We have some grades on way to Norris Lake, TN where I had to keep it in third gear and was managing 30 mph. This was with the cargo area pretty full but only 350 lb total passenger weight.
I found the specs for our 2011 Yukon AWD WITH 6.2 L V8: Trailer Wt: 8100, Payload 1622, GVWR: 7300, GCWR; 14,000.
So it does sound like GW payload is not any greater, and the GCWR is only 1000 lb more.
I am thinking that the 10,000 lb tow rating is more a product of the strength of the connection of the hitch to the frame, than the torque and horsepower of the 6.4 L V8; and worried that I won’t see much improvement in towing performance, especially with a full car!
Where did you find the GCWR data for the Grand Wagoneer?