92 shadow es power loss

2.5 turbo mpi ok..... car is sluggish all the time but but the main problem is it runs fine for 20 min then its like i just have no throttle floor it and it takes off like a bat out of hell.does the same under a load or going up hill .ive replaced a lot, timing belt,injector harnes,map,tps,checked converter,fuel pressure 55 psi or better,replacing injetors today. did have a wast gate leak but know its fine.changed plugs, wires,dist,coil,hall effect. it hasnt brought up any codes.but i know the engine light works I can make it come on.im boosting about 15 so i know its nothing to do with the turbo.have fine air flow.will put in new injectors today and see what happens.ANY FEED BACK WOULD BE GREAT??????!!!!!!!!!!!!!!!!