Nelsonlwn....I have a 2004 5.3L that had Syntec in it until about a week ago. I sent the Syntec for UOA, but it is lost in the mail. I would be intersted in your thoughts on Havoline. I have M1 10W30 in the 5.3L now, but I have Havoline 5W30 waiting until the M1 is depleted.
I have wondered about GC in the 5.3L myself. Here is my UOA with Castrol GTX.
Thanks for the UOA link. I dont have any "objective" data on the Havoline yet. I will have a UOA on the havoline in a couple of weeks, as I have about 500 miles left before my oil change.
Some subjective observations: I changed from the factory fill to Havoline 5W-30 @ 50% on the OLM (4000 miles). I immediately felt a smoother engine and the gas mileage increased. Thought it might just be breaking in well. When the OLM said to change, I took the Suburban to the dealer because I had a free oil change coupon. They used Quaker State 5W-30. Almost immediately , I could feel that the truck seemed sluggish. I changed out the Quaker State and put back in Havoline 5W-30 at 56% OLM and again felt a smoother engine and better gas mileage. I am now down to 8% on the OLM and will do a UOA on the Havoline.
I am really looking to using GC with all the excellent UOAs on here, but I am going to wait until I see the results of the UOA with the Havoline.