Its when accelerating to shift up gear, possibly judder is giving the wrong impression of the problem. It is a more of a severe hesitation. if I didn't know better I would say it is like running out of petrol and hoping that it will just go a little bit further before it packs in.
The problem is also reminiscent of my first few cars where I had a throttle for cold start, depending on too much or too little throttle the car didn't run well until it was warm.
This however happens whether the car is cold or running for a length of time. The only other odd thing I have noticed is the sound of water tricking which is coming from the passenger dash area, very strange. No leaks anywhere just the sound of tricking water.
No warning lights at all which is why I am making the query as I would have expected the car to detect this problem. You can drive for a couple of days and it doesn't happen then for the next 4 its all the time. I have had the car regularly serviced and they have also looked at it they cant find the fault until a light come on.
Some months ago on a couple of occasions the car wouldn't go into 1st first for the whole of 1 day and has been fine since.
I have had this car from new. Hope any of that garble makes sense