slow DNS resolution
Solution 1:
I strongly suspect that you have a broken firewall between the DNS server and Internet that drops long DNS responses that are normal with DNSSEC. Try running dig with "+dnssec" option and see if it starts timing out too.
Cisco PIX/ASAs, up until very recent versions, are known to behave like this by default: https://supportforums.cisco.com/thread/2013390.