hi all,i,ve got an issue with my 2006 pre facelift 2.5 manual sorento.when im towing my caravan im getting an awfull lot of black smoke from the exhaust when im accelerating.its not so bad when cruising but still there.when solo it still happens but not so bad.its just had an oil and fuel filter change and i,ve put redex through but no joy.it sometimes feels slugish then it will pick up.does anyone have any ideas what might be up?i thought egr valve but not sure.any ideas would be great.thanks kev t