52 plate vivaro 1.9 DTI intermittant cutting out ?

have spent thousands on this van this year. one problem after another. so far had new turbo, full engine rebuild, had my hp pump pump rebuilt, injectors reconed, new rear calipers and new front discs. now I have an intermittant fault with it cutting out mainly when you want more fuel to pull away. drive it gently and alls ok but put your foot down at say a roundabout and it stalls. turn off key and back on and all back to normal. had the MAF changed, pump solenoid, crank sensor and fuel rail pressure relief valve. any help gratefully received