Internet browsing is too slow behind TMG 2010

Dear all,

I have a problem with TMG 2010 on Windows Server 2008 Standard R2 (Domain Member) where the browsing is to slow behind it and I have to refresh the site twice to open and it takes a lot of time to complete loading. 

The NIC configuration as the following:

1. Internal: IP address, Subnet mask, DNS
2. External: IP Address, Subnet mask and Gateway.

Notes:

1. VPN access it enabled
2. Download speed is normal and I can reach the max without no problem.
3. Accessing sites from TMG Server itself is better than the other clients
4. I am not using Web proxy setting in the browser just use the TMG as a gateway in NIC configuration of the clients
5. I have used Connectivity Verifiers to AD, DNS and External Website. All of them are fine and no alerts from them.
6. I have checked the Binding order and internal NIC is on the top.
7. I have disabled Web proxy, HTTP Compression.
8. I have disabled NIC Offload

• netsh int tcp set global chimney=disabled
• netsh int tcp set global rss=disabled
• netsh int tcp set global autotuninglevel=disabled