I have an '03 Alero with the 3.4. 210,000 on it. I have a misfire on cylinder 2 that only happens at high rpm, usually past 5k, and only happens on the 2nd to 3rd shift if the shift delays. If the shift happens right away there is no misfire on that cylinder. I've ruled out the fuel pump and filter. 55psi even while misfire is happening. ICM and Coil packs are all good, plugs are brand new, wires are new. I tested every single sensor under the hood and they all check out. I did an exhaust backpressure test and the Catalytic Converter checks out so it's not plugged exhaust. I will mention that the intake is barely seeping at all 4 corners, again
Any thoughts would be good. it still runs and drives fine unless i am accelerating hard, like when you go to pass someone.