We have 2013 Audi Q7 TDI (3.0l). We are tow a 21' Holiday Rambler Campmaster with dry weight 3600lb. We travel with mostly empty tanks, so a loaded weight of less than 4500lb (just a guess). We use a weight distribution hitch but no sway control. The Q7 handles it like a breeze, and I am never short on power. Usually on highway the rpm stay below 2000 in either 7th or 8th gear. I have never felt a sway issue even on stormy days.
On our last road trip, driving from Edmonton Alberta to Seattle Washington then to Vancouver BC then to Jasper AB and then back to Edmonton, we averaged about 14mpg over 3600km with a lot of driving through the rockies. Drive down fron Jasper to edmonton on a calm day was almost 16mpg.
I have to say I am very happy with the Q7 as a tow vehicle.