Someone, with much more knowledge of me… (Bryan???) can explains me this system. I’m driving only with D(irect) but maybe in the slow gear I need to use it…Maybe?
‘D’ = drive, 4th or top is the overdrive ratio IIRC 3rd is direct 1:1
Hope this helps
Sorry maybe I’m liitle stupid…Can make me an example? The 2D i put when i run to go in 5th more fast and the 3D in Little space…Sorry for this orrible explanation 
I think what you are saying is that you are using the ‘J’ gate side of the gear lever? Manual control of the gears will not increase the acceleration of the car. The transmission control unit will do the work just as well as anybody can.
The XJ40 only has 4 ratios but 4th has a lock-up feature which happens <>88kph from memory.
Using the sport setting will raise the RPM ointment when the trans change to the next ratio.
Hope this helps, please keep asking if you are still unsure.
I’m not sure too…if you can make me a pratic example…some situation when i must/Can use this 2D and/or 3D… 
There is no must use situation, if you want to change the gears it is your choice, for example going down a long hill you can use 3 or 2 to make the engine slow the car instead of keeping the brakes on all the way down.
Going up hill if the transmission goes between gears for example 4 to 3 to 4 to 3 then you can select 3 and keep it there until you feel the car will hold a steady gear.
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Now I understand…I write exactly because I had some difficult to gear going up 
but sorry for my stupid question…must I change the gear from D to 3 or 2 when i’m moving? 
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Only if you want to ‘play’
If you are in a situation where you DO NOT want to plant your foot but want to increase speed quicker than the gear you are in will allow then drop down manually.
For situations where you want maximum acceleration then just floor the accelerator pedal and let the engine management do its thing.
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I shift up and down all the time and only use the brakes occasionally, but that’s just MY style …the ZF tranny is a joy to use!
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