I buy the ones with the highest written millage warranty at Costco. If I don't get the millage out of them, they discount my new ones. You may have to get a manager involved but they will stand behind them. Think of it this way. If they are guaranteeing you 40,000 miles, you're prob gonna get it. Make sure it is in writting and keep it in the truck with a copy of the dated receipt and installed millage. They cost more, but with the miles I put on it end up saving me money.