Well, I might as well regurgitate my preferences! LOL
I'd been using M1 since the 1980s, even proved those old commercials of them draining the engine of oil and they kept running. Sometime around 2010 M1 quit being a Group IV oil.
I noticed in my first two trucks that they would rattle a lot on start up with M1. After the 4th oil change I sent in an oil sample for analysis. Then switched the trucks over to ACDelco's full synthetic (5W30). No more rattle. After the 3rd or 4th oil change another sample was sent to Blackstone Labs to compare the two.
M1 had a lot more metal in the oil compared to ACDelco and the latter didn't cause the motor to rattle on start up, no more oil usage between changes and a slight improvement in mileage.
Several years later ran the same tests comparing ACDelco and Quaker State Full Synthetic and surmised them to be essentially the same performance wise. You be the judge, here are the oil analysis:
The Sierra's comparison is between ACDelco and Quaker State Full Synthetic:
On the Yukon's analysis below, the 2018 and 2019 oil samples are Mobil 1, ACDelco for the other three.
It is my opinion that what makes these oils better than M1 is their rating under ASTM D445 where their viscosity numbers are over 11.5 (100 degrees centigrade) or 66 and above (40 degrees centigrade).
