Looks good! You're fortunate to have received such a nice ride as your first. I'm impressed that your first plan of action is to make sure it's up to par before diving into the mods. i don't recall any teen with their first car asking about this, but how many subs and how big of wheels can they fit, etc. Then you see a kid on the side of the road with big wheels and a squat from the sound system, Skar and Punisher and IG handle stickers on every window, broken down from worn and failed powertrain, drivetrain, suspension or steering components.
Fortunately, this generation is arguably the most reliable of GM's trucks. The LS engine is relatively simple in design and easy, clean and cheap to work on. You've also found a forum where you can be walked through damned-near anything on your Yukon.
To start:
1. How many miles are on it?
2. Know any of its owner or maintenance history?
3. Any warning lights on the dash?
4. Any gauges reporting anything concerning?
5. Anything that doesn't work or works improperly?
6. Does it make any seemingly odd sounds?
7. Any concerning suspension or steering feels?
8. Suspension noises?
9. How do the brakes and the brake pedal feel?
10. How's the transmission's operation?
