Powerloss on high speeds (z19dth)

[genesisfm]

Hello,

I got a problem, when i drive more then 120 km/u and i want to speed up i feel something like a fading* (up/down) and the car speed up a littlebit.
When i drive 150+ km/u the maintenance light is coming up and the engine stops for a moment (untill i drive 130 km/u or less) and the light is going off.

This is only on high speeds or on the 5th or 6th gear.

Ps. i have a automatic gearbox.

*fading = what i mean with fading = normaly you feel the car wants to speed up, but i feel a speed up 1 sec and then speed down 1 sec and then speed up .... speed down.. The car speeds up but not fast a normal.

My question, did someone over here knows the problem?

Thank you.

Rob