This thread caught my eye as I notice my last contribution was in 2010 and by then I have not towed with my then new car. We have since given up caravanning and moved over to a motorhome. However having towed with my then 59 plate Sorento which I did for nearly four years I never felt it was as stable as my previous model which had SLS. It was much more powerful. I don't want to exaggerate as I could tow at 60+ (if I wanted to) on French motorways but felt that at 60 and over it would be less stable which was a good incentive for keeping the speed down to a reasonable level!
You might have seen my recent post about similar problems with my Sportage.I have just fitted the Grayston rubber Spring Assistors,took about half an hour. Haven't had the caravan on the back yet, but others tell me it will make a significant improvement, and only £16 a pair from local Caravan/motor Factors.
I think the next step will be to upgrade the rear springs - if balancing the tyres does not cure the problem - There are some springs that fit inside the original ones. Will have to check out the price of those.
(PS. I have been towing for over 10 years - last car was an X-Trail - loved it - before that a Mondeo) At the moment I am NOT loving the Sorrento.
We had a 56 reg Sorrento, followed by a 59 Titan, both were excellent neither had SLS. Now have a 2012 KX2 which is also an excellent tug!
I agree with David Klyne, all of them could tow at 70mph in France safely. ( Before they changed the rules!)
Now tow at 60 mph where permitted, perfectly stable.
------------- DS-There's more to life than football!!!