caravan towing/better intercooler

I recently started towing my caravan again but with my defender td5 , I was wondering if anyone has uprated thier td5 with a larger intercooler and if so which one (so many out there)

it currently prefers to cruise at 50mph and struggles with long climbs

I have a Discovery TD5 automatic. Have upgraded mij cooling with allisport oilcooler to stay in Temperature control. The power is oke have not felt the need for more power. If i were to upgrade i would do so with allisport, good service, good quality an they will always answer questions.

Ok thanks