I had a 95 silverado with a 5.3L that I ran to 189000 miles before I traded it in. I ran Valvoline 5W-30 also. It ran as good and with as much power as the day I bought it.
Why?
Well my nieghbor is an off road race mechanic. He builds, tunes and maintaines a custom off road race vehicle that is worth over $100,000.00. He uses Valvoline and has never ever lost a bearing, rist pin, or even found a tiny bit of metal in the oil when he changes it.
Thats good enough for me. I do know that you better run 5W-30 in it, or any warranty you may have will be voided. And you will more than likely cause damage at some point, when is the question, and how much will it shorten the life of the engine.
Happy Trukin!
Ed Crabb
sbjake@molalla.net