This is the problem that i have:

When i drive normally , i dont press the accelerator FULL everything is ok.
When i press down full without the kick down everything is ok too.
But
When i go around 80km/h and i press full together with the kick down and the revs go up past 5000rpm, on 5000rpm-5500rpm there is a kind of jerk that the car does. Like as if there is no petrol reaching for a second. I dont know maybe something is dirty, injectors are dirty? Is it a problem with the gear box? Should i change the gearbox Oil?

Is the air to fuel ratio rite? Or maybe i should change the fuel filter?

Did anyone have this problem? Can you please advise me on what to do, because i am worried that it is the Gear Box.

PLEASE LET ME KNOW GUYS!