As an added point for people (this may have already been posted but I didn't go through all 7 pages of posts).

Double check your performance by tracking your mileage. On our Tahoe, tracking mileage ofer time showed that I got a consistent 10% bump in MPG using midgrade (89) vs regular (87) but no further bump in MPG using premium (93). Note this was over multiple tanks and multiple driving conditions. Since the cost of higher grades is typically $0.10/gal/grade, at $1.00 per gallon this wasbreak even, at $2.00 per gallon I was saving $0.05/gallon by using mid-grade and at $3.00 per gallon I'm saving about $0.07/gallon. The manual states regular is fine.

So, do the experiment over a few tanks. Your car might not benefit, but it did for me. Plus tracking your MPG regularly will also tell you about the health of your engine. If it starts going down, something is wrong.