AMSoil has API certified oils, and will NOT void your factory warranty. Even if the engine suffered a failure as a result of the oil AMSoil (or any other oil company) will pony up the money to repair the problem. Why don't you research a provide proper information over incorrect information, or worse...hearsay.
http://www.syntheticwarehouse.com/api_licensing.htm
On the topic of 'high mileage' oils? There is nothing different over the additive package, and no reason to use a 'blend' or a 'high mileage' oil over a standard dino, or synthetic at any time. And synthetic trumps any regular dino oil at all times. The additive package is far more stable and keeps the engine protected from advanced stages of wear and heat stress for far longer.
I've stretched as far as 15,000 miles (AMSoil) on a single oil change without any issues whatsoever. In fact I'm on 7500 with my last change of Pennzoil Synthetic. I'm going to try Castrol or Royal Purple next. Also in point of fact there is less and less basis for changing every 3000 miles, especially such if the oil has a plainly better lasting additive package. You'd be wasting your money to buy the better oil, and change it every 3000 miles.
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