dave cos4x4

I was driving my mates scooby,my 99, and noticed that if i stayed at a steady speed eg. 40 , there is a hesitation,it's as if i have taken my foot of the throttle,if i accelerate the problen goes away,it's only when trying to do a steady speed.
When i got home he said that it has done this a few times but comes and goes.

Anyone any ideas what it is and also where to take it to get fixed and tuned in the North West area.

Thanks ,Dave.