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I am sorry that you have not been helped yet. I just came online and saw your question
Is this a caravan you have towed before with this vehicle without issue, or did you just start towing this caravan for the first time?
Not knowing the history, I do need to ask if you verified that you were well within the weight limits of towing with your vehicle, which does include passenger weight and cargo weight in the vehicle as well as anything stowed in the caravan
Any issues with going uphills without towing
Any smoke out the tailpipe while you were going uphill
Did you notice and loss of boost pressure on the boost gage
Please remember that I am not there and therefore rely on you to provide as much detail as possible. thanks
Having a boost gage would have definitely helped in determining if the turbo is even working under aload. I am not sure I can help at this point so I will open this back up to other experts.