Loss power, slow accelerating, turbo

[Asibasi]

My name is Asen and I own Volvo VNL 2008, Cummins ISX 400 truck. I have bought it second hand with bypass EGR. The truck used to have perfect power initially for the first three months, and then the problem started.I recently checked EGR valve, and it is still bypass. It used to use 6.5 ;7 M/G.Now the problem is that the truck has not enough power to go over hills.In addition, it uses way too much fuel.-4.5 M/G when i am empty. Fourteen different mechanics already worked on the truck, and they couldn't solve the problem. In my opinion, the problem is associated with delayed delivery of the fuel to the cylinders. I have changes many parts ( Inter cooler turbo, turbo and timing actuator, timing sensor, crank shaft sensor, U sensor, boost sensor, back pressure sensor, camshaft, and I have also replaced tested second hand injectors) The fuel pump pressure is perfect; it pumps out , but the truck doesn't have power. I put accelerator to floor but engin not power and working quite.Turbo when I am go to hillup boost and go to 0, then boost and go to 0.