What's up with my combo 1.7di 2003 ?

Hi my van feels like its running out of fuel it's shakes and judders when I'm driving, but has no starting or ticking over probs I changed the airflow and did a full service including diesel cleaner in the tank and filter but no joy,it's got so bad that it now has no power on hills or when I have gear in the back until it gets to bout 3000rpm and then it still judders ....
Help would much appreciated !!! Cheers Lee