I have several older Chevy Blazers, all with the 350 in them, and run 89 octane in all of them. A couple times I thought I would save a few cents and put 87 in, and developed a small miss or chug. I worked at a repair garage back in the 1990's and folks would come in and say their vehicle had developed a miss or was hard starting. We would always ask them where they had purchased gas and what octane, almost always they had got the cheapest gas in the area with lowest octane rating. We would tell them to drive the car and run the tank low and fill back up with a higher octane, usually solved the problem. The Unimarts in my area were notorious for cheap and bad gas and still are.