What feels like stuttering

[Motegi22]

When cold, my prelude doesn't seem to run very well. It seems to have a few flat spots (or what feels like) between 2k-4k.

When its fully warmed up, its much better, but you can feel it "stuttering" around 30mph in 4th/3rd gear.

It had a cam belt change 3k miles ago by previous owner, could it be anything to do with timing?

Its a 1999 2.2vtec manual and always run on v power. 100k on clock. Recent major service 500 miles ago failed to cure problem (ruling out sparks, oil, fuel filter).