i have a 2000 z24, whenever im driving once the car gets to about 3000rpms its starts misfireing like a biatch. it only does it in the cold tho, if its like 50 or so out it runs fine. i changed the plugs but have no clue what else it could be??

Could be Coilpacks, or a failing ECU

Could be a plugged/restrictive fuel filter. If it gets too restrictive, it allows the pressure to drop too much as the RPM increases, effectively starving the engine of fuel. If you haven't changed it recently, try that first. Fuel demands will be highest when cold, so that's when it will likely first indicate an issue.
Sometimes it's the simplest things...

the last time i changed the fuel filter was just over a year ago.. could it be f'ed up already? the next thing i was gonna do was coilpacks but ill do fuel filter too and see.