I bought treated lumber from Treadway's and it already needs replaced...three years old.
There's no guarantee t will stay pretty, just that it won't rot. There's a difference. If you don't have a protective finish on it, it will weather and look older than it is. If it has rotted after ony three years then I would take it back to the retailer that you bought it from, if that is possible or at leat tell them about it. They should want to know about it or replace it so they can let their supplier know that it might not have been properly pressure treated.