my dads 03 Gt has regular boltons and bassani X-pipe w/ side exhaust cat back, after x-pipe install w/ MILs the car was great for about 7 months and check engine light started to come on.the light was o2 related. We went and got it tuned and the code was saying there was a slow response from the rear oxygen sensors,very similar to or is exactly this code (P0153 Upstream Heated Oxygen Sensor circuit Slow Response - Bank No. 2.) I need to get the exact number but this is what it said. The dyno tune included turning off the rear o2 sensors from the computer so the tuner said to remove MILS since they were no longer needed and this might fix the light. It didnt after 3 days its back on. # were 253rwhp/300rwtq after tune if this helps,full CnL intake,x-pipe and catback and custom tune??? any ideas?