I had gotten a warning catalyst depleted followed by an increase in fuel consumption from 18MPG standard highway to 13-14MPG. City is 8-9MPG, tire pressure 36psi, running a snorkle, TUFAnT steel rims 18", all services done, engine runs like a chimp, spark plugs new, exhaust is quiet and idels smoothly, cleaned throttle body and MAF.
So long story short at 14MPG your catalytic converter is most likely ineffecicient. Maybe not enough to throw a code yet but getting close.
I bought a maganaflow drop in replacement V8 left right bank and will let you know if it restores fuel economy. Things i tried unsuccessfully:
1. using liquid mechanic to clean catalytic converter, only seemed to work as long as you pour it into your fuel tank,
2. installed downstream oxygen sensor spacer nope didnt work but removed the code,
3. installed spacer with, integrated catalytic converter found on ebay, nope now code is back,
4. cleaned oxygen sensors by soaking them in gasoline, and MAF cleaner, nope didnt work,
5. replaced downstream oxygen sensors, nope didnt help,
6. installed electronic chipped MAF and a chip tuning OBD2 plug thats supposed to provide more power and up to 3MPG better fuel economy, nope didnt work,