As others said, look for a stiff link, and measure your chain for stretch (wear).

You also asked if 2,500 miles was OK life, and while it isn't great, it's fairly typical for hard riders in hilly areas. The higher tension involved in climbing increases the wear rate, so you'll likely never see the kind of chain life that someone riding in flat landscape will.

Going forward you might want to use two or three chains rotating them every 1,000 miles or so. If you're chain still has life in it, replace it now, but save it for when the new chain or chains catch up in wear condition, then rotate it back into the mix. The advantage of rotating multiple chains, is that it keeps the chains and sprockets better matched for their life cycle compared to running each chain until it's replacement point then starting a new chain.