low power on my diesel van?

ok.van will start and tick over fine,,will tick over all day if you let it..then i start to drive it..it seems fine for a few minits and i lose power..pull over pump throttle and picks up again but not for long,,do i need new diesel filters..injecters are fine as is pump etc,,only had this van a week or so drove home 30 mile and 3 miles away from home problem started,,any help would be great thanks,,dave