Thanks for all the input guys. The manual is kind of confusing as well. It goes on and on about 0W-20 being the oil that the 5.3 engine was tested and created with. But then in another section it states that you need to use a "Dexos 1" approved oil but says nothing about the grade. I had 8 quarts of Castrol Edge 5W-30 so I used it. I guess I just got paranoid reading so many people saying that the engine was speced for 0W-20 for a reason, or that I'd be ruining my engine because the EcoTec was radically redesigned from the previous 5.3 engine. Hence it "required only 0W-20".