Musician who love the contrast -> comparative exactness of mechanics - and recently auto diagnostics (lab-scopes CANbus GMLAN woohoo for now!) having just gotten my first truck/vehicle newer than 1994.
I was very surprised to discover that OIL is a VERY deep subject!-)
GMT400 - '94 Silverado NV4500 trans has AMSOIL (75-90 i'll check)
Gen1 - '89 Geo and '91 Firefly trans have Pennzoil SYNCROMESH
GMT610 - 2010 Savana (my first OBDII woohoo!) has mobil1 5w30 currently - thinking what to use (?) as new to me