was the fuel system bled after? baka hindi properly filled with diesel yung filter so pinasukan ng air yung fuel lines. this will not happen if your mechanic filled the filter to the brim. this trapped air can cause some of the injectors to miss prime causing uneven engine run. may "tik-tik-tik" na sound ba, especially if coming from only 1 or 2 cylinders? pump up the fuel pressure using the manual pump on top of the filter then bleed off each injector by loosening the high pressure fuel line nut until only fuel comes out.