movano 2.5dci

I have a 57 reg movano 2.5dci, it started cutting out and had diagnostic which said high pressure fuel pump, this was changed however it now drives fine up to 2500rpm over this it just cuts out, turn ignition off and on and away it goes again. In addition to the pump we have changed the common rail sensor switch, had the ecu set checked out which was all fine, checked all wiring to ecu and pump, replaced air mass sensor, we do not know what to do next
Up to 2500rpm it will drive fine all day but go over it and it just cuts.... anyone got any ideas... any help gratefully accepted

movano 2.5dci