Auto gearbox
 

How many gears are in a automatic gearbox on a CDT, The reason I ask is when I am towing in Drive it drop the revs when it reaches around 52. This cause the car to struggle to pull properly and blow black smoke, if I change down to 4 the revs come back up and it tows lovely leading me to think it is a 5 speed auto box.

It is indeed a 5 speed box

But it should change down to 4th if you push down gently on the accelerator or lower if you push harder. I sometimes manually change down when on the motorway rather than kick down to stop the engine revving too much (mine's a 2.5 KV6 though).

Un-intuitively put the box in sport mode.
This move the rev band up the scale - i.e. gear change ups will occur later at higher revs.

Go quicker is the simple answer. They are much happier towing at 60mph (even better if you do 60mph according to a sat nav).
They are very reluctant to kick down and will struggle until it has to kick down due to speed. So either use 4th or up the speed.

I was under the impression you can't/shouldn't tow an automatic:shrug:

I think the OP is talking about towing something rather than being towed.

yep i thought so cause it will destroy the auto box

You can tow an automatic but you have to limit the speed and keep distance as short as possible.

Towing an auto
 

SFAIK a suspended tow is OK ie the driven wheels off the ground and not turning. Anything else and there are speed and distance limits and I had one car where the handbook mentioned adding extra ATF fluid to the box. So, a flat loader or a suspended tow is the best way forward. What does the car handbook say?:shrug: