The gas you buy at Walmart gas stations is not top tier gasoline.
Although the gasoline at Walmart is still high quality good gasoline that runs fine in your vehicle the gasoline from Walmart is not top tier gasoline.
Top Tier gasoline is good for your vehicle and can help extend the life of your engine as it helps to clean the valves and pistons and removes carbon deposits.
Running Top Tier gasoline in your vehicle helps remove those carbon deposits which in turn helps improve your fuel mileage.
Your engine performance will be much better as well.
If the gasoline is Top Tier gasoline their should be a sticker on the gas pump saying that the gasoline is indeed Top Tier gasoline.