I got four new ACDelco O2 sensors from RA a while back. They came in Delco packaging but no extra padding inside. The sensor ends all had anti seize, all four rattled around big time inside their box. Two were Hencho en Mexico, two unmarked to their origin.
I think the timing is adjusted to give it more top end, but that's just a guess, since I installed the tune on both the silverado and the yukon I sometimes get a little ping out the gate depends on how long it has sat idling or not, I need to send a file back for both trucks. both have a sport tune.
Most likely they have the knock sensor riding the spark advance tables. That means the spark will advance till the knock sensor senses knock then it will back off the advance a hair till no knock is detected.
Hope that makes sense. I do have a problem with my writing skills.
I had read somewhere that Denso supplied GM with O2 sensors, among other electronics. I suspect GM sources their O2 sensors from a number different vendors. I know the four sensors I got came from two different places of origin.
I would bet all the money in my pocket that the quality of the two ("ACDelco" and "Denso") are identical.