Hyundai Tucson CRDI Acceleration Problem

I have a Hyundai Tucson CRDI 2007. Recently, my husband left the radiator open and the car overheat. The cylinder head had to be removed, new inhaust & exhaust valve we placed.

After that, it seems to run okay then suddenly stops when the car reach about 2000 rpm. My husband thought it was due to the battery, so he bought a new one.

The car didn't run for several day, my husband just kept starting it. Changing the battery from our other car then it start. When he check the engine for leaks. The fuel filter was leaking. He had it replaced , the car run better and starts easier. But then when he reach 2000 rpm, the engine dies again.

The parts we've replaced so far are inhaust & exhaust valve, bearing, air filter & fuel filter.  I've uploaded the pictures of the engine, you might recommend something to us to resolve this.                    

The technicians we're not aware on how to resolve the problem, only my husband got the engine running. He is also the one who suggested to had the fuel filter replaced.

It also seems that the engine stops when it reach a certain temperature and rpm.

Any input will be much help to us. I'll you guys posted.