Intellisense has been reasonably flaky for me in 2013, it seems better than last versions, but it seems to work well for a week, then get really slow for a day, then speed up again. I don’t think anyone here has been able to understand why it gets slow sometimes, it works well 90% of the time.
Most of us at epic use https://www.wholetomato.com/ to navigate the engine source files, it seems a lot more responsive than intellisense generally.