Main thing to do is, LOG it first stock.

See where you can find areas of improvement based on your car, and the fuel in your area.
Some cars want more timing, other cars want less timing. Same goes with fuel. Its easiest to do on a dyno...where you can repeat the runs, and the cool down times between runs, and look the graphs to see where you made improvements or not.

You can pick up a lot on those cars now. It seems GM isn't leaning on the tunes as hard as there were out of the gate. Maybe due to fuel?

TM is an issue with those cars,
Funky Fuel trims also common,
Horrid MAF signal, another issue.

Best of luck!