won't pull past 5000rpm

[datdrift]

idle from warm and still doing it when hot, i don't think the choke works, cos its never idled higher than around 1000rpm.....could be an air leak, but all i changed was the fuel filter and one fuel pipe so i dident disturb any boost pipes......
in second gear its more like 4 - 4500rpm that it hesitates at
anyone think of any parts i should try changing as ive got a few spares