For completeness sake, I thought I would answer this with what I found out.
There was a few different errors occurring here. First, I was trying to use TLS1.2 which is not supported by Windows Server 2003. Second, I am using host headers which are not evaluated at the point of the certificate handshake (unless you use SNI which is only supported by IIS 8/Win Serv 2012) so I was not getting our internal certificate but our default wildcard cert issued by Comodo. Finally, there seems to be an issue with the Comodo certificate chain on our server (seems to be missing one of the root or intermediate certs).