my car has lost power..not too bad on flat, dead uphill?

My Rover 45 diesel turbo has lost power. If I am going uphill, I have to put on hazard lights as I slow right down. On the flat in top gears I can get up to 70+ but hit a hill and I am way down again. Disconnecting air flow meter did not help. Has the turbo gone, how would I know? Could one of the injectors be leaking..how would I know?? Does it have a catalitic converter, if so what does it do and could it be dead? would I be ebst to get a diagnostic done?