MSSQL Connection times out on first attempt.

I have a production environment with an MSSQL 2008 server and two domain controllers running on Server 2003 and acting as the DNS servers.  The environment had been working fine for about 2 years - but recently I started having a strange problem.  When I try to connect to MSSQL I get a timeout on my first attempt, but connect OK on my second attempt.  My workstation is on the domain and using the two DC's as DNS servers.  This seems to be DNS related.  I hang up when connecting to the direct IP, or the server name, but on management studio can get in on the first attempt   using the FQDN of p21sql.ivd1.local.  Other domain users are having the same problem.  In addition some are having very slow connection times to web sites (but throughput is fine - so again I think it is DNS related).

The same problem occurs using my ERP system which connects to the DB server.  I get a connection error but connect on the retry.

I am not using dynamic ports on SQL, and 1443 is open on my Sonicwall and on the SQL server firewall.  The firewall is temporarily off on the workstation.  

I'd appreciate any troubleshooting tips.

Thanks