Volvo 850 2.5 20V 170 hp has no power

Hi, I got my Volvo 850 2.5 20V with 170 hp again the nen buddy now about 2.5 years, because he does not need it anymore, but somehow he has no power. In advance, I bought the car about 3.5 years ago, according to Tacho he had run at that time about 310T the KM counter stood but there already, then I drove about 25T and my buddy 2.5 years loosely 75T, so he already ran clearly over 400T. The engine still runs as I got it at that time, he really did not have power at that time, he runs with downhill and back wind 170 to 180 KM/h and does not accelerate really fast. The tooth belt is new a year ago, my buddy had made it once and spark plugs also, it can not be that, the engine runs very well, I would say, no clapping in the stand he really runs great and very calmly grasps like a thick V8 am therefore really surprised. Oil consumption was and is still very high 1 liter on 1T he does not have a clue about the performance.