My nissan pathfinder yd25 cylinder head got internal crack na was successfully replaced. Easy key start, however, engine very weak/low when accelerating both to reverse na forward. FYI the car is automatic diesel engine.
With no smoke we'll assume the turbocharger is ok.
If the car thinks it is in neutral it will behave like this, the ECU won't allow full power in neutral or park. It's worth checking the plugs on the gearbox to make sure one hasn't come loose.
Also, air in the fuel system can cause trouble. Please try this: find the primer bulb (under the fuel filter usually) and squeeze it a few times. Is it quite firm? How many times do you have to squeeze it to make it firm?
Can you connect a diagnostic tool to the car and see what boost pressure you are getting when accelerating from 0km/h to 60km/h with your foot at 50% to 75% throttle? You should be seeing 18psi or more.