After checking all the fluids and underside for large leaks, take it for a drive that will get you all the way up to 70mph. You want a route that will take you through turns in both directions at 30-40 and 50+. If the steering wheel starts shaking or the front end picks up a shimmy/wobble, time to get it up in the air and start checking parts. Being 15 he's a new driver and an unexpected wobble can be scary and disorienting which i've seen cause accidents on older GM SUVs.
If you want a nice project truck to work on with your truck, you've got one. Any old truck is going to have a whole host of maintenance items that need attendance. It all depends on how involved you want to get with the truck. It can take you into engine repair as one of the beginner level repairs.
If it loses oil and you don't notice a leak underneath that would equate to the amount of oil lost, combined with poor fuel economy (sub 14 highway, sub 6 city) fouled/oily spark plugs and the smell of oil in the exhaust, you're looking at the plenum repair. I've put a couple writeups on here pertaining to it.
Coolant flush through the engine and radiator (do not flush the heater core, don't even drain it) can help remove silt in from the engine and promote proper cooling and heating. Thermostat should be replaced as well (removing the accessory drive bracket that holds the alternator and A/C compressor is the easiest way to do this). Serpentine belt should be inspected, idler and tensioner pulley should be inspected as the bearings start going out at your age and mileage. Pull the wheels off and inspect the brakes front and rear. After driving 10 or so miles there should be no rust on the braking surface of the rotor. If there is , you're likely looking at pads minimum (only go semi-metallic if you are going to load it up or premium ceramics if you aren't going to load it with anything) also be sure to inspect the calipers, the bleeders should come loose (either 8mm or 3/8ths?) take a pry bar and pry the caliper out away from the center of the vehicle, if it moves and you have slack, the slide pins are good, if not you might be looking at new calipers/caliper brackets. On the rear, you'll want to make sure the wheel cylinders are not seized or leaking.
Some creature comfort upgrades any young man is sure to enjoy (I know I did) are as follows.
Get an aftermarket bluetooth radio with the according wiring adapter. If you want to give the speakers a boost, it involves some custom electrical to make it work well, but its worth it, at the age of these trucks the speakers just suck anymore. Putting LED lights in the dome and map lights makes for a bright cab at night when trying to find something. You can replace the drivers map light with a red LED so you can use it at night and not blind yourself. Steering wheel spinner knob is optional, but I won't go without mine, forget the autozone garbage ones, goto TSC for some quality. If you want brighter headlights, Sylvania SilverStar Ultra are brighter and more clear than OE while maintaining original beam pattern and focus. Do not just put LEDs or HIDs in the stock housing, the pattern will be off and you will blind other drivers. Lastly, killer steering wheel cover, nothing beats a killer steering wheel cover.
