Howdy all, i have a 2004 subaru impreza wrx with a sti swapped motor. Stage 2 tuned on 93 octane. After i put a set of good aftermarket headers on to replace the stock exaust manifold that was completely shot everything is sealed from engine block to up pipe to turbo and from turbo to down pipe all the way to the back of the car. I installed what i thought was a working upstream o2 sensor and found out it was faulty sent it back,then got same one that worked. After it was installed it have been throwing CEL here and there not consistantly, (code is p0133 or slow response i have obd scaner in my car to run the computer and clear the standing and any pending codes). After i do all that the motor is still very hesitant on throtle response. Cleaned mass air flow sensor in my perrin short ram cold intake tubing, changed all plugs and coil packs. Just did oil change last week was running and idling normal for half a week then started to hesitate once again all fluids are good and the right ones needed for my car. No turbo leaks, vacuum or anything of that nature in an way had everything checked. But soon as it starts to accelerate at times, in traffic, stopped at a traffic light or try and backup car tends to want to stall but slowly corrects its idle RPMs, can anyonr please give me some insite to what the real issue may possible be from my explainition...