renault trafic 06 no power until 2500 revs?

can anyone help i have had this renault trafic van about a month now and it runs fine doesnt miss, starts ok but the power seems to die when i change up a gear. when the revs are at about 2500 it seems to pull ok but soon dies again when going up hills.i have been told it could be air flow meter but unsure does anyone have any clues? thanks.