I currently own a 1978 280z. I recently replaced the fuel pump, fuel filter, and cleaned out all the lines and gas tank due to it running extremely lean reaching 4k RPM's. Now as i try to push the car harder into the 5k RPM range it starts to lose power and the RPM's drop then kick up then drop again. This has also been happening in any RPM range when ever i floor it. My thought is the new fuel pump is sending too much fuel(or not enough) and there isn't enough air getting into the engine because it has a stock air-box which i cleaned out in hopes of fixing something but I had no luck. Ill post a video of the problem as soon as possible. Thanks.