Had a DA CN7901 chain since Aug 2013. It came with the (new) bike which is full DA7900. I decided to order a new CN7901 chain as a spare/replacement as I couldn't get it be silent in 15th gear. I noticed the original chain had a fair bit of stretch in it in comparison to the new one.

Should a chain not last a bit longer than 2-3k miles? I do a lot of hill climbing and powered gear changes are sometimes needed.. is this why the chains stretched?