its more than likely your mass airflow sensor, on nissan engines, if the mafs goes bad the ecu goes into limp mode, thus not allowing it to go past ~2500-3000 rpm.
(@ least i believe your car has a mafs)
1993 nissan 240sx hatchback(stock) <<drifter, straight liner, road courser
"Horsepower is the force that determines how fast you hit the wall. Torque is the force that determines how far you take the wall with you after you hit it."
"Horsepower sells cars, torque wins races" - Carroll Shelby
"Real cars don't make power at the front wheels....they lift them."