I use 89 octane. Have been since I've had my truck. As far as I know, 89 should be fine unless the Chevron gas with techron is messing with the engine seeing it's a cleaning agent and all. I don't know, I just feel that under heavy acceleration or heavy load, the engine really shouldn't be clicking and tapping that loud and that long. I'm just afraid something is going to snap or break eventually if I don't figure out the problem soon.