Just replaced my EGR Valve (it was broken), the one I took off was 30% clogged with tar. I have had poor performance for 3 years (but OK ish), with new clean valve it goes like a bomb. When I got mine it had done 60k, now 110k. Wish I had known this sooner. This could be the cause of the lowish power and it takes about 2 hrs to do. You will need
1) Latex gloves - its dirty
2) Carb Cleaner, lots of rag, old toothbrush, and a small scaper
3) Set of allen keys, I think the one you need is about 8mm
4) Torks bit set.
5) Few small sockets, ideally with a bendy bit.
Looking from the front, you have a manifold on the right, under this is the EGR valve, under that is the anti shudder valve.
First separate the anti shudder valve, then the EGR Valve. Then say OMG when you look inside. You may need to release the steel water pile above the alternator to get enough room to unbolt the pipe from round the back of the engine (just so you can move it, no draining needed). Clean and refit as before.