Hiace Disel losing power/running rough

Hi, I have a 2010 Hiace Diesel 2.5l van which loses power/runs rough at if I put my foot to floor, high revs, going uphill etc.
The Toyota dealer replaced air filters but hasn't made any difference, before I take it back and they fleece me again, any ideas what could be the problem?

Thanks in advance

Fuel filters ok?

thanks for the reply. I don't think they checked them no, is it easy enough to do myself?

Yes easy to do, but also easy to create an air lock/leak. Give it a go.

Or

Any garage will be able to do it.