have a 05 trailblazer with mult codes. Recent plug and coil change ( ac delco 41-103) as was running rough and reduced lite on before plug change. Now with P0068 that occurs with reduced engine lite also, and p0304, and p0300 at times. I can reset, and will be looking at cylinder 4 again. I did save freeze frame info if needed. also did clean TB and relearned.