Hi Cathy, I have the same car (KX3 Auto) and found similar problems My previoustow-carwas a disco 3 which had a nose weight limit of 150KG andwhen I checked the nose weight of the caravan it was 115Kg which was way over the 85kg limit for the Sorento Auto when I altered the load of the caravan and got the nose weight down to near the limit it towed much better,Ithen decided to fit some "M A D" rear springs which helped the car to keep the car level and whilst it will never tow as well as the Disco it tows fine as long as you keep it below 65Mph.
Regards
Doug