Off-throttle deceleration and fuel consumption

Question I've been meaning to post for a while . . .

Now it used to be, whenever I was decelerating with the throttle closed in the Charger (i.e., engine braking), my narrow band O2 gauge would drop to zero (digital gauge). I understood this to be normal, as to say the computer was cutting fuel with the throttle closed. But at some point, something changed to where the gauge only goes to zero if I'm off-throttle above 3000 RPM. Anything below 3000 and the gauge cycles like normal. No codes, car runs very well, only other symptom to speak of is a slightly wandering idle, between 900 and 1150 RPM according to the digital tach on my timing light. The factory tach is dead accurate when compared to the timing light.

Could this be a TPS issue? Is there even an issue to begin with? I'm just wondering what changed.

Do you have a scan tool that can look at injector pulse?

I can borrow one, yes.