just bought a 2015 suburban ltz, not much of a mechanic ever since getting kicked out of auto shop class in high school but I have a Masters in youtube.com mechanics. Im looking to do some performance upgrades to my vehicle...where do i start????

 

A tune will be your best bang for your buck. Don't waste time/money on silly stuff like a cold air intake.

After that, the only way to see actual/real gains are things like a cam swap or forced induction.