I had a stumble at 1/2 throttle with no code.Pulled the 02 sensor out of the
LT's & found 1 sensor black.replaced it & the sputter went away.
This was a pretty basic diagnosis but it threw no code,I assume the heater
was bad.Just thought I would share this info.I was advised by my tuner that
the sensors can go bad & the pcm will compensate until it cant anymore.
I f did not pull the 02 & seen it to be black I would still be messing around
with the car instead of driving it.