Check your compression . Any drop in compression will hurt the performance. Is you car losing coolant? Is it casting any codes ? If so what ? Was there any misfires before you changed out the plugs and coils . If so you may be dealing with back-pressure from the catalytic converter. Raw fuel in the converter can cause it to plug and a plugged converter kills power . Also do you have an aftermarket tune on the car . Change out the air filter as well so it can breath Just a few things to look at . Hope this helps