ClearOS 7.2: Internet Browsing So Slow

Dear All,

I've just upgraded my machine from ClearOS v6.7 Basic to ClearOS v7.2 Business. The settings are:
- Web Proxy Installed with Non tranparent mode and No Authentication
- Egress firewall installed: Block all, allowed this port: 80, 443, 993, 53, 465, 587
- Incoming firewall open port: 81

I've installed it on sunday and browsing run flawlessly. However on Monday morning, panic happened. Users browsing activity was very slow. I have turn off virus filtering also deeply URL analysis also protocol filtering (egloo) but still internet browsing very slow.

I've also bypass everything in web proxy/content filtering like office365,com, avira-update.com, etc. But still web browsing still slow.
Web browsing run fast for a while when I click RESET CACHE button. But then web browsing run slow again.

Please advice me how do I solve this problem. is it make sense to disable PROXY CACHE?

Any help is appreciated.

Regards,
Faisal
I've been using ClearOS since 2008.