My car had the oil consumption problem.
I changed the oil pressure sensor/switch (on top of engine) and that helped.
But I still had the DoD problem. So, after I got the transmission re-built, I had it tuned out, and its run great ever since. Now I only need to put 1 quart in between oil changes, not 2.
Congratulations on your new 8-9 year old Monte. most of them don't make it to 140k on the original transmission, do you know if the tranny has been re-built or replaced?