VSphere ESXi 5.5 Windows Guest Network card not active after reboot

In short, it sounds like a networking problem.

But... TMG's rule configuration might slow it down due to URL Filtering or DNS resolution interacting badly with your rule setup. For example, if your rules governing DNS resolution accidentally included a Domain Name Set that required DNS resolution, that's a Bad Situation to be in.

So the easiest way to identify whether that's an issue at all is to make a rule set that requires minimal processing, optimized for speed:

• Globally turn off URL Filtering if it's enabled
  • if MRS is responding slowly, that'll affect the first access to any given URL
• Create a rule Allow All Outbound From TMG To Anywhere
• Create a rule Allow Web Protocols From Internal to Anywhere (assuming you have an Internal network defined as your inside subnet)
• Create a rule Allow All Internal as Allow {TMG/Internal} to {TMG/Internal} - because it's a DC and cutting the DC off from the network is often Suboptimal

These rules should be ordered at the top of the Access Policy list, before any other rules.

• Disclaimer: These rules assume a multi-NIC TMG setup with the Internal subnet configured correctly, and most likely an external firewall. IF IN DOUBT, HIRE A CONSULTANT THAT KNOWS TMG.

This combination will skip any DNS resolution for outbound traffic. If the situation is 100% improved by these changes, try changing one thing at a time, apply the change, and then wait at least 5 minutes to ensure it's had time to take effect before deciding whether it was helpful, hurtful, or didn't make a difference.

11Mb/s is too close to 100Mbps to be only a coincidence. It's clear that you have a problem with one of the network ports, either on the switch or on one of your servers's NIC, not being set to 1Gbps/full duplex. There's no doubt about that. The question is which one.

Make sure all your NICs are set to 1Gbps/full duplex, and that every single port of all network devices between all of your servers and storage devices (switches and routers) are also set to 1Gbps/full duplex.