Why wont my transit go more than 55mph??

My 03 plate Ford Transit 2.4 Crew Cab has no power, am lucky to get 55mph, already had timing checked, valves checked, new fuel lines and filter, new AGR valve. The last person to repair it, says no faults are coming up on the computer. It doesn't smoke, but struggles to start every morning! What do i do next??? New Turbo or Fuel pump?? PLEASE CAN SOMEBODY HELP ME, I'M TEARING MY HAIR OUT!!!!