I had exactly the same problem. Was getting the Yellow "Service Engine Soon" idiot light. Took it in and the Dealer ran the codes and got P0420 and P0430 which they said indicate the Catalytic Converters were bad--both of them. No one believed that since the truck had less than 10k miles on it. So, they reset the codes, but a couple of weeks later they came on again, and stayed on. Went through this several times, taking the truck back to the Dealer multiple times where they checked everything including the O2 Sensors. Finally, they just replaced the two Catalytic Converters under warranty. I mentioned the O2 Sensors but they told me the sensors for the Catalytic Converters were integral to the Catalytic Converters. Since then no Service Engine Light.
Only thing anyone can figure is I was getting most of my gas at a Commercial Station that sold Non Ethanol Gas. They sell lots of Regular, but probably very little Premium, which is what I was using. Possible they got contaminants in the Premium Tank which because it didn't turn much I was continuing to use. I now buy gas (Premium Ethanol) from stations where I know they get lots of turn on their Premium Tanks. Usually it's Shell.
