fuel problems

[MARTIN C]

Hi I have recently bought a 1996 300tdi discovery and having a problem with fuel system, when changing gear at high revs the engine loses all power like it is being starved of fuel, if I remove my foot from accelerator for about 5 seconds after a cloud of white smoke from the exhaust it's ok again, have replaced the fuel filter and lift pump but still have the same problem, anyone got any ideas please