Carbon buildup is a known issue on those vehicles. While we have not tested methods for carbon removal in your application, the product best suited for that task is likely the B-12 Chemtool Total Combustion Cleaning Kit (part #2610), which is introduced via a manifold vacuum line. This means it comes in contact with the air system as well as the intake valves and combustion chambers. If you choose to run this product, please let us know of your results. Good luck!