You know, I have spent alot of time beating this subject to death in all the GM forums....About what oil is BEST for TBI, you know. There is alot of rave about synthetic and alot of talk about the dino oil. I use just regular old dino oil, whatever autozone is having a sale on...Which lately it's been Peak 10-w30 and STP oil filter for like $16!!! Basically, I tried to analyze every type of oil to find a clear better, but basically I think it's all jibberish. I think all dino oil is basically the same. The only reason I haven't gone full synthetic or whatever is because my truck is 200,000 mile truck. Even though I have a relatively new engine and tranny I'm skeptical about changing it up since it's been so used to dino oil.
I figured what was more important than finding the "perfect" oil, was keeping it fresh and changed. I do the filter everytime I change the oil and keep a strict eye on the color of the oil. As soon as it looses that transparency and goes more black, I change it regardless of miles or months it's been since the last change. Which usually it comes right out to every 3 months I change, since I don't drive the truck 24.7, and have other DD vehicles. Before I started using Peak, I was using Pennzoil strictly. I don't even know why. I think my HS shop teacher swore by it and it stuck with me but now, just whatever. I think it's all the same.