Freelander 1 Lumpy and doesn't want to rev when cold

Hi
2004 TD4.
Now I've replaced one of glow plugs it starts really nicely (all 4 are ok), but I've still got a the problem that I've had for years is, for the first minute or so it just doesn't want to rev, at 2k it's really lumpy, if I really hit the throttle it will pickup and once driven for a short distance it seems to be fine, it's like it's full of leaves and needs a good rev to clear them out.
I've bypassed the EGR and all the pipes are good., vacuum and intercooler.
I tested the injectors last year and they are under fueling but I can't find anyone that can tell me if the amount it's under fueiling will actually cause an issue.
Any ideas or are they all like this?
Thanks

It's a diesel, it's power output is controlled by how much fuel is added to the air going in. If there's only enough fuel for it to rev to 2k, then it'll only rev to 2k.

so what's the issue, it's fine when it's warm?
It will rev past 2k but I have to really hit the throttle and why is it so lumpy at 2k?