Just bought a 2006 Chevy Tahoe and don’t
know what kind of oil is in it. Still has about
70% life left. What oil does it take?
Conventional or synthetic? 5w-30? Or can I
use a thicker grade since I live in an area that
the temperature can reach 115 degrees?
Proper oil specs are on the dipstick, maybe inside a breather cap, and in the owners manual, available on line. If you're concerned about what's in the engine, change it. Adjusting to different weights shouldn't be done except to adjust for engine wear.
5W30 will work just fine even when it is hot.