There appears to be an issue on some machines where certain network adapters can contribute to the game running slowly, hitching a lot when doing common things like opening/closing inventory, and voice over playback not playing when it should.
We're investigating this issue on our end, but some of the folks in the community suggested disabling any extra network adapters you may have, such as Hamachi, VMware, VirtualBox, or your corporate VPN adapters.
To do this, visit the Network Connections control panel on your computer and try disabling one extra network connection at a time and try running the game to see if you still experience the issue.
More information is available in this forum thread:
Update, May 28, 2015: This item should be fixed in 1.06.