Cisco Firewall :: ASA 5505 Very Slow Speed - Can't Open Some Websites

I just installed a Cisco ASA 5505 in my company's network,however the network became so slow and many websites cannot be opened or it takes toolong to open (yahoo, hotmail etc.) resulting to a request time out sometimes.
 
Here is my configuration:
 
ASA Version 8.2(1) !hostname xxxxxxenable password xxxxxx encryptedpasswd xxxxx encryptednames!interface Vlan1 nameif inside security-level 100 ip address 192.168.1.1 255.255.255.0 !interface Vlan2 nameif outside security-level 0 ip address

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