check your wires no matter if they are new or not i dont care just check them by pulling them one at a time and listen to the motor to see if it makes a difference on how it is running. if your cat is bad then you can test that by getting under your car and hiting it and see if something inside it rattles. as far as tune up how abotu a cap and rotor have they been replaced. i think i am having the same prob but mine just kinda hits certain spots in the rpm range that it kinda laggs and then it will hit a "good" spot and go and then it might hit another. they are all below 3500 rpm. when it gets to like 4k its go time.