I had the exact same codes on my 06 gtp and i had to have my rear cat replaced. The thing about the shop is they have a more advanced computer and if the codes are on the car when they check the car their computer will tell exactly what cat needs to be replaced. I also had a transmission pan seal replaced due to a leak. But since the cat was replaced I havent had any issues with a misfire now i have more transmission issues... I will figure those out but that is the insight I can give you about your codes. Good luck if you have any questions you can ask and I may have an answer and if I dont I will figure it out.
Painted Wheels/Calipers/Center pieces
Tinted Tail lights
CAI and Crabs
Vinyl over Chrome trim
Eagle Eye Headlights
Painted recessed Grilles
Embroidered floor mats and seats
Bought my G6 for temporary 6 months to a year. Now I fell in love and i would die before getting rid of this car.