Sounds as if you may be drawing air into the fuel or have fuel starvation..
How sure are you about the lift pump?
Is it a genuine one or a cheapo substitute that might need an adapter?
If there is a fuel return pipe from the banjo nut on the filter head, take it off and clean it till you find the air-bleed pinhole, and clean that properly.
Take the fuel feed pip, off at the injection pump and prime the fuel pump lever. (may need to turn the crank half a turn). When the pump lever is is operated fuel should positively squirt out the pipe at the injection inlet end. If not, sort it.