poor running and starting on half a tank or less daf 45 1996?

my 1996 daf 45 150 will not start unless u crack the injectors with anything less than half a tank i have changed the filters and keep it topped up including injector cleaner to which i thought the issue was solved until i had to do a long run and i got to half a tank and it started hesitating i pulled over filled up and was perfect again