Syntec oil exceeds manufacturers requirements, so no impact on warranty. Just better mileage/performance. And yes, tranny fluid change is by the manual (think it is at 70K miles? Have to check manual) But also very CRITICAL w/all newer GM autos (and others) is anti-freeze/radiator fluid change.
The GM Dex-cool antifreeze installed at factory is sometimes called Dex-Kill, by mechanics!! It works great, but if you don't change it at 40-50K miles or 4 years (whatever comes first) it becomes highly acidic and corrodes gaskets,waterpumps and the radiator itself. Also gets very sludgy. COMPLETE flush needed and it only takes about 30 minutes! No need to get crazy and remove freeze-out plugs or anything........just a good, thorough flush!