I have a 2004 envoy with the 4.2 I replaced the plugs and coil packs 6 months ago and it has run perfect. I went to start it up las week and it ran like crap. I put my code reader on it and got codes for the cam position sensor and the vvt actuator solenoid. I replaced both. Now I onlt get the p0300 code and it runs horrible. Any ideas? Anyone? This has been a great vehicle and I can't afford to replace it.