Recently installed a new Dell Optiplex 960 running 32-bit Windows 7 Enterprise. The system board includes an Intel 82567LM-3 network adapter. With the latest Intel driver from Dell, version 126.96.36.199, the card would frequently lose connectivity for two seconds (e1kexpress events in System event log). When it reconnected, it would often be at 10Mbps instead of 1Gpbs. Also at startup, the card apparently did not connect fast enough, which led to various errors (DNS lookup 1014, NETLOGON 5719, Time-Service 131, group policy failures).
There is some confusion as to whether System Idle Power Saver (SIPS) causes this issue, and whether SIPS is available on the 82567LM-3. It is not exposed in the driver settings.
Upgrading to the latest driver from the Intel site, version 188.8.131.52, did not help.
Rolling back to the base Microsoft driver included with Windows 7, version 10.5.1.0, does help. No errors and consistent 1Gpbs speed in 39 hours since rolling back.
Intel threads discussing this issue: