My 02 wrx is having a strange problem under acceleration. If I pull out of the drive and punch it. It'll accelerate close to smoothly out of first, maybe hesitate once or twice in second, stutter for a good bit in 3rd then smooth out and accelerate smoothly after 5000 rpm. then fourth and fifth gear i don't want to talk about. It's almost like it's stuttering badly at full throttle but when I ease off to about 75% throttle then it accelerates more smoothly and quickly. If I'm in 5th gear and I give it any gas to accelerate, it stutters. It's throwing a speed sensor code and an 02 sensor code but I don't know which 02 sensor and their 130 a piece. Please help me diagnose this. I'm not sure if its misfiring or if it's a boost leak because some times the boost leak would be a constant problem at any rpm at any speed and it's like the stuttering is getting worse at speed.