First off: have you double checked your actual mpg rather than just going by calculated values to see what you're actually getting?
Second: what effect do catless DPs have on the o2 sensors? I know most will throw a cel without the corrections made in your tune to over ride the cel, but what else? I assume the sensors still function correctly, just outside of their normal limits correct?
At 13k mi you SHOULDNT be having any issues with sensors, cats aren't an issue because you don't have them any more, and although EGR could effect mpg and/or mpg readings, you should be 100k miles from issues there as well.
This leads me back to your o2 sensors, not that they're bad, just that they haven't been told to look for new limits yet, so your computer thinks they're running extra rich = poor mpg. If this is the case, your actual mpg (miles driven divided by gallons used) should be much higher than your calculated mpg.
As an example, when I bypassed the EGR on my mazda, the EGR valve was taking in fresh air instead of exhaust, so as I hit cruising speed and the ECU leaned out the mix by adding EGR catalyst and advancing timing, it thought I was getting much better mpg than I really was due to higher o2 sensor readings than the ECU expects. It says I'm getting 36mpg when I'm only getting 24. The opposite of your problem.
Has LMS incorporated your downpipes into your tune?
Taparalk'd...expuct typoz
