ok i have a bone stock 05 gt with 15000 miles not sure what type of oil is in it now i plan and changing it soon and also i'm not sure what octane to run some of my friends say 87 is fine since i don't have a tune but im not so sure.. i have seen a pretty close race on these forums over royal purple which i have used before and mobil 1.. which would be better to use with the car having 15000 miles already??
Any synthetic 5W-20 will be an excellent choice. I recommend Pennzoil Platinum, Quaker State Q Synth, or any over-the-counter synthetic 5W-20. Mobil 1 used to be a true Group IV/PAO synthetic basestock, but ever since some gas chromatography tests revealed the use of Group III (highly refined dino oil) synthetic base stock it has confirmed my suspicions that Exxon Mobil is now playing on the marketing hype of "synthetic". For engine oil, I recommend over-the-counter "synthetic" because it is affordable and you can safely conduct 6000-7000 mile oil change intervals with most brands without worrying about engine damage. Audi and BMW specify 10k mile oil change intervals (regardless of time) with their oils and engines.
There's nothing wrong with Group III base stocks other than when they are priced as Group IV oils.
For drivetrain stuff like gearboxes, transmissions, and differentials, I recommend Redline and Royal Purple. They have a great reputation for making excellent products at decent prices without resorting to multi-level marketing/pyramid schemes like Amsoil.
For fuel, I recommend a quality 87 octane fuel. Find high volume gas stations that a lot of people frequent. Costco and Sam's Club are such locations, and Meijer if you have them in your area (I forgot to check your location). I find that sticking to a high volume gas station is more important than brand or if it is a "Top Tier" gasoline.
If you get a tune, you may want to use 93 octane but I would recommend sticking to 87 octane tunes to allow more flexibility and to reduce your operating costs.
