Car pauses before moving

I have a 2002 Ford Focus 2.0i Ghia automatic with around 30,000 miles on the clock.
Recently I noticed that there is a small jerk when going from first to
second gear. I checked the fluid level and it was overfilled (must have always been) but only by around 1/2 litre. I removed the 1/2 litre and it has improved some but there is still a 1/2 second pause after I press the accelerator then the car gives a small jerk when going from first to second.
I have not noticed this before, is it normal?
It is fine if I accelerate quickly but I am concerned that this could be the start of a small problem with my tranny. The fluid looks okay, it is a little bit darker than I would have expected but it does not smell burned.
Wanting to be kind to my car I am planning on using Royal Purple in it because of the reports I have heard. I know Ford now recommend 5W/20 for all Ford Focuses so the motor oil seems fairly straightforwards. I see that the tranny requires Mercon V fluid, does anybody know whether Royal Purple ATF would be up to the job and if so, what type should I use? Whilst I am asking, what is the best coolant I should use in the radiator?
Also, the tranny is a 4F27E ... I would like to change the fluid but do not see a drain plug, am I blind or something? I assume it is not necessary to remove the pan and that changing it 2 or 3 times will flush out most of the old fluid. If somebody can explain how it should be done that would be great.
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I forgot to mention that this only happens in hot weather or when the engine is hot.
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i had a mazda one time that done something like that and it turned out to be the coilpack breaking down
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Flintstone wrote:

into second gear there's a jerk. because if you're stopped and you push on the gas pedal and there's a pause like maybe the throttle plate in the throttle body is sticking and then it releases and off you go, I've had alot of sticking throttle plates. under warranty I've just replaced it. Usually right on the can or bottle aftermarket fluids will say if they are compatable with manufacturers products but I'd stay with mercon V. Most modern shops have trans flushing equipment that does a far better job that drain and refill. but I can email you detailed instructions. And you're not blind we use the cooler line connection at the trans cooler left side of radiator to do the trans flush. snipped-for-privacy@hotmail.com
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