vivaro dti lwb?

Hi all. where do i start. I have a vivaro on a 53reg, its been off the road for 8 weeks now and reallt starting to p**s me off. The issue is,,,,,,, starts fine , runs on the spot for hours but as soon as you drive it it cuts out. If you drive it hard it dont but if you drive normally it just stops dead, flick the key on and off while still moving and it will run again fine for a few moments.

I have had a brand new injector pump
Brand new fuel rail
Brand new pressure sensor
Brand new cam sensor.
Brand new fuel lines
Brand new fuel filter.
The tank has been taken out washed out.
The in-tank pump has been cleaned and works as it should.
I have bypassed the filter housing just incase it was cracked but still no joy.
I have done a leak off test on the injecters and they are fine.

Someone please help i would be most greatfull
thanks jon