Fuel issue?

Not long had my high pressure fuel pump and x4 injectors swapped and recoded with genuine donors off a 2nd hand engine, along with a full flush and tank off job to remove any metal particles.

The car is still behaving weird though cutting out sometimes once starting, so you need to rev it in first once cranking over then the engine stays fired up. It makes a strange juddering in 6th gear and sometimes the low gears when crawling.

I did take it back to the mechanic when it was first doing this and he didn't seal one of the injectors properly, causing a strong fuel smell and smoking from front and rear. Thats gone now, just the other symptoms persist.

Another strange one is when I brim it with diesel now, it has just started reading less than 400 miles for a tank. Usually it says 540-545. 

Hope someone can help.