Just installed some 20s with new drilled rotors and ceremic pads. Car shakes pretty good at mid speed from 40 to 70mph. At first I thought it was the rims but if it was a balance issue wouldnt I notice at low speeds? I put the car in park tonight and reved it up and when it hits 4000rpms it pops not like a backfire but like it missed a cylinder or something. I recently replaced wires and plugs along with a new PCV, air filter, and both O2 sensors which my engine light still came back on. ANY AND ALL IDEAS PLEASE? Very frustated right now.