I had a similar problem a couple years ago with my car. After changing the cap & rotor that i purchased from a local auto parts store my car had no power and wouldn't rev past 3000 rpms i was like wtf. Then after almost an hour of trying to figure out what went wrong my bro and i started back tracking our steps, we double checked the cap it looked fine then the rotor, after further inspection turns out the rotor was defective. We put the old nissan rotor back on and the car ran perfect again. Bottom line please only use quality nissan oem tune up parts on your car. The berk-arnley cap & rotor that i purchased was crap and cheaply made, which made my car run like shit. Since then i have only used nissan caps,rotors and fuel filters on my car. Live and learn!