I have a 2006 g6 about 80k, about 6 months ago it started acting up. Very subtle at first, slow acceleration, "chugging", rpm going up and down even when at a constant speed. I took it to a GM dealership and gave me the following codes P0420 catalytic converter low efficiency, P0010 Intake cam actuator solenoid circuit error. They told me that it is a camshaft positioning sensor. No mention about the cat converter. Told me it would cost about $450 for labor plus parts. Another repair shop said it's probably the cam actuator solenoid and that it should take about 1/2 an hour to replace, but the parts costs $190. Any suggestions?