Drew99GT,
I've seen advertisments in the car magazines about using Mobil 1's version of 5W-20 weights saving gasoline annualy. Now I seen M1 "green cap" 0W-30 indicating as a replacment for all oils in the 5W catagory going up to 30W.
To my knowledge GM has not indicated anything about allowing such oils to be a replacement for the old 5W-20 through 5W-30.
I wish I could try/use a 5W-20 in my 08' Impala SS but the dealership doesn't have it in synthetic to try it. Perhaps my engine wasn't designed to use a 5W-20 overall it's best to stay with the 30.
Durango