vauxhall vivaro?

hey guys, who can help me.......... new high pressure pump, new low pressure pump, new cam sensor, new crank sensor, new air mass meter, new fuel lines, new injectors, new boost selanoid, new speed sensor, new fuel filter housing, cleaned out fuel tank.................. why have i spent so much on these shit vans, right the problem i got is it dosent start on the key. It will start on a bump or easy start! Once running if u let it idol after about 10 seconds it stops and u got to go through the same process to get it going. When i get it going if i hold the throttle at around 2000rpm it will run all day long. But if u go to drive it u can pull away but as soon as u get to 2nd or 3rd it cuts out like someone has turned the key off,,,,, if u flick the key on and off while drivng the fault goes away for a few seconds.
I have checked all the wiring on the gearbox and when i do get it running i wedge the throttle around 2000rpm and have a pull and move the wiring around the engine bay and it does nothing so wiring must be ok.....
It comes up with '' low fuel pressure '' on the scanner.
If any one could help or sort it i would pay them as i am up to £2100 and it still dont go................ There got to be some one that knows as Vauxhall dont know anymore than me.......................... Thanks jon