Hi,
can anyone please help or point me in the right direction please?

I have a S reg Ford Focus 1.8 petrol. (S509 K**)
The car starts on the button all the time and idles fine.
When cruising at speed on motorways, say between 65 and 75, (no hard accelerating or erratic driving) there is a an intermittent hesitation in the throttle.
The power will die off for a second, drop a few mph and then kick back in. I do not move my foot on the accelerator and the a.c. is off.
It only does it at higher speeds, runs fine around town etc. It is mostly annoying at the minute but I am thinking it is a warning that something is about to pack up.

I have searched the site but I can only find low speed and accelerating hesitation.
Any info would be greatly appreciated.

EDIT... It is stock and has no mods

Thank you.

Lewis