I am a firm believer in pretty much any AMSOIL oil product and I use their fluids in my 97 vette (engine, trans, and diff)...however, that being said, I dont believe AMSOIL has the GM certification on the oil.
Does the oil meet the certification, yes, but has it been tested to the certification, no...

And because my Solstice is under GM warranty for the next 5 years, if anything happens to the engine while I'm using AMSOIL, they are going to throw a hissy fit. I'm just going to stick with Mobil 1 Syn.

Over on corvetteforum, the guys there are convinced that Mobil 1 synthetic forumla has been changed recently (within the last year or so) and that it isnt as good as it used to be...however, it still carries the GM cert...

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2008 Base 2.4L Manual
Sly Exterior, Black Top, Two Tone Interior
Preferred, Premium, Convenience Packages
Monsoon, Floor Mats, A/C
GXP Dual Exhaust/Fascia

Future:
Sport Metallic Pedals, Spoiler