Well.......
In mine, I put in normal dino Supertech 10W-40 (I have found Supertech 10W-40 to be on the thin side, made general mental note "Supertech oil is on the thin side.")
I am next thinking of trying GC, or Castrol Syntec 0W-30, in there. Even 0W-40, depending. Maybe.
You can run almost anything......
I was going to put in Redline 0W-20, but that's pretty overkill for a 4.3...
I also hear Castrol GTX 5S-30 is a darn good oil for a 4.3.
OK other 4.3 guys?
*My engine model year of Vortec 4.3 is 1994. Same mechanicals as 1995. Is in pre-1996 Vortec category, but 1994/1995 are supposed to have had the best heads from pre-96 Vortecs, as pers10forum.com lengthy thread...