I'm no expert but I would say the problem is not with your fuel filter. Having said that, for the cost of a replacement (less than 20 quid) and a 5 minute job, it's worth doing anyway.
I don't know this particular engine, but it's probably more likely that the injection pump needs setting up, as many have a max speed adjustment on them as well as idle adjustments, etc. It's really a job for a diesel specialist in my opinion.
Hope this helps.