Website Error 504 Timeout Issue

My website (www.dellamarshall.com) is incredibly slow at times and now often I get an error 504 timeout message. I spend about an hour with tech support at HostGator trying to fix it and the support person eventually said the problem is with the Highend theme and gave me this link:

http://spam.hgfix.net/790055.txt

Can you help me get the website running faster again?

Thanks