Recently my '53 plate ex-RAC van started losing power at just below 3000rpm. I asked a local garage to change the fuel filter, check the EGR stuff, the turbo actuator rod and if those made no difference to stick it on their diagnostic machine and figure out why.
They changed the filter and told me that they'd checked the stuff I'd asked them to... which turned out to be "not true!"
Dan T on the forum runs In Transit Services in Strathaven near Glasgow and checked all the things he thought it might be before settling on the turbo actuator rod. A few glancing blows with a lump hammer and it was all fixed and in the process of fixing it noticed a few other things that needed attention and sorted them too.
All in all a great service and I can't recommend him highly enough!
http://www.in-transit-services.co.uk/