I have read that the rear O2 sensors do about 10% of fuel trimming compared to the front O2 sensors. Its called FOASCO or FOCSAO or something like that. If Monodax was up I would be able to tell you.
I have turned of reporting with no apparent issues.
So far as the "blackbox" PCM code, its all there, its just that the tuning suites dont list all of the available parameters. Talking with a GM engineer who did calibrations for these trucks, he commented on there being many many parameters hidden in the Tunercats VDF's, let alone the EFILive ones. But he still tuned a Vortec 350 for just over 4000rwhp and 430rwtq with a Whipple and marine intake.
peace
Hog