1991 Toyota MR2 loss of power

I have a 1991 toyota mr2 turbo. The car has 294000 miles on it but the engine was rebuilt and only has 48000 miles on it. My car is completely stock. Im only running 7 psi. If I drive normally it runs fine, no problems. However if I accelerate hard it runs good till 4000 rpm, when all the sudden my power cuts out. I have noticed that if I back off of the gas the car accelerates harder. My car picks up faster with less gas. I know that the turbo is spooling properly. I'm not getting boost creep, and its not compressor surge. Whenever I give the car more gas it goes slower, and when I give it less my car becomes a beast. Mechanics I have taken it to say that the timing is correct. I have replaced the fule filter, changed the oil and replaced the plugs, wires, and cap and rotor. Any help would be great. Thanks