Huge packet loss Hyper-V when guest is running with R410 and Broadcom BCM5716C NetXtreme II

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http://serverfault.com – I am running a domain controller, that also has a Hyper-V role installed. Within the Hyper-V, I have a legacy Windows 2008 SBS that we will eventually retire. When the guest OS is shutdown network traffic is normal. When the guest OS is running, there is huge packet loss (around 50%, in bursts of 5 seconds on and off). I am running Windows Server 2008 R2 fully patched, no antivirus, two NICs (one for the native machine, another for guest VMs) that plug in to the same switch. Hardware is DELL R410, NICs are Broadcom BCM5716C NetXtreme II running the latest drivers from the Broadcom website (HowTos)