2003 Volvo 660 with Cummins n14 truck turns off while running, then hard to start

with the rpm's fluctuate it goes up and down then my truck would turn off ill get it to start after a while of trying. Start rolling and the rpm's would just rise and fall on its own then I would have no power in the pedal. I would push the pedal down and nothing would happen then my truck would just die. I just changed the ecm it cost me 2000 bucks and still nothing. He also changed the timing sensor and changed a few fuel lines near the tank. He also bypassed a few hoses near the ecm and made a straight line from the tanks I believe that go straight into the fuel filter. Idk what goes on. After all the the truck worked for like 5 hours no problems. Then on the highway my rpm's jumped and had no power in the acc pedal, I just down on the pedal and nothing at all and it just died on the highway. I waited a while to start it back up and it start then died waited longer again. Started up heard some unusual clicks coming from the rear of the sleeper and under my dash board. Idk what that was either but it start led again got it to move then just died again and no just keeps doing that. Seems like after a while of sitting it'll start up run for a little bit then die again

2003 Volvo 660 with Cummins n14 truck turns off while running, then hard to start