There are a lot of low friction ring problems. Not all vehicles with low friction rings have oil consumption but some do. I suspect this is the case if the PCV valve isn't the cause because GM has had issues with lower friction rings on some engines.
Some of the earlier Northstars had ring issues, GM redesigned the ring pack in 2003.
But, It wouldn't be a bad idea to soak the pistons with some cleaner while the spark plugs are out.
-Get the engine up to operating temp.
-Remove all 8 plugs.
-Rotate the engine to where no piston is at TDC.
-Buy 2 bottles of Piston and Ring Cleaner, P/N 12378549.
-Distribute 1 bottle to the right bank & one to the left bank.
-Let the cleaner sit in the cylinders for at least 2 hours, But NO MORE than 3 hours.
-Place some heavy towels over the left & right spark plug holes, Turn the engine over several times with the starter to evacuate the cleaner from the cylinders. (The COILS should be on your work bench during this, You do not want any spark!!)
-Reinstall the plugs & coils.
Warm up the engine thoroughly......And RUN THE [censored] OUT OF IT!!!! I mean REALLY BEAT on it!!!! It will not break, This engine loves to be ran hard.