Just want to add that GM is in business to sell vehicles not lubricants. Their engineers may spec out new specifications for lubes but it is chemists from additive suppliers and base oil producers that actually do the formulating along with people from lubricant manufacturers. Believe what you want about the differences/advantages/disadvantages of a syn. vs. conventional but my $$$ goes to the synthetics. Sure, in meeting the new API specs many oils may claim to utilize a synthetic base but in reality it is most likely a group 2 base oil. I could go on and on about the benefits of syn. but you need to decide for yourself.