I completed the Primary AD DC from 2003 to 2008 R2, setup and moved the DHCP to 2008 R2. I changed the primary DNS setup in DHCP property to the new 2008 IP address.
I did not not demote the 2003 AD DC yet. I shut it down and realized the Internet access became extremely slow.
I can't think of anything that I have missed to complete the migration. Please help!