l332 4.4 transmission overheat flashes up when towing

hi all hope someone can help i have a 2003 l332 4.4 and when i ve been towing my caravan for 25miles transmission overheat flashes up but when caravan is not on you can do 300 miles and does not come on plus have seen coolant coming from the waterpump area ,temp does not go over 1/2 way thanks

water pump leaking.

gearbox oil and filter change