ok, i have an 83' turbo 280zx...high rpm, under full throttle, i have NO power. I have full boost, it doesn't sputter or jolt...well, low rpm, full throttle, it sputters...but high rpm, full throttle, full boost, NO power...i hate this. I've also noticed a slight backfire when i coast down from mid to high rpm...if anyone could give me any advice on this, it would be awesome

 

It doesn't sound like a fuel problem, how about an air flow problem. You might want to check the air flow meter. The flap might be not be able to move freely enough to get enough air. Also air filter?

 

How are your plugs? How old are they and how old is the diz-cap? Coil? Could either be bad timing, weak ignition, or poor AF ratio - which could just be tuning, injectors or fuel pump.

If the cat is dead, let the car idle for a couple minutes and look under the car, if its glowing red it is finished/clogged. Bang out the materials if you dont care about smog, or buy a new one. It can also do this though via fuel or timing problems making the exaust very hot.