Loosing power after 3000 RPM

Hello, have problem with my rover 25, in each gear its working fine, there is a good power, but its good till about 3000rpm, then engine gets noisy and it feels like that car gonna dress out. Problem is as well when u going uphill, it loosing the power, for example, if u driving uphill and u have about 2000rpm and the pedal is in the floor, it stays around 2000 and nothing more! Just done the head gasket. Any suggestions, fuel injector, clutch, transmition, maybe somewhere at bottom of the engine? maybe some checks which i can do at home? thanx.