omega b 2.0 16v runs round but has no more performance ???

Hello guys! I really need your help!!! And I do have the problem, with which Omega it runs quietly, but has no more power. You can drive maximum in the second gear. In the third gear it sucks off completely. Incidentally I have already made a lot of new on the car. Because I have been quite pulled over the table. Newly made: KAT spark plugs air filter Complete exhaust return system Krummer cold running system valve cover seal cylinder head seal comes the days. Maybe one of you can help me. I don’t have a plan anymore!