After trying over 20 different versions of the Pro1000 drivers for a Dell Optiplex 755 that has a Pro1000 integrated 82566DM-2 chip - I found one that works and does not drop the connection and provides full throughput. I uninstalled it from the Device Manager and then scanned for changes, then updated the driver manually by selecting the folder for my OS using the driver set below:
This is from the v13.1 6-17-08 release - it includes support for Pro1000 cards up to 82574L, 82567, 82567LF-3, 82567LM-3, 82567LM-4
Whomever knowingly looked the other way while folks were forced to purchase new operating systems or even computers because of this problem should be voted out of directorship of Intel or terminated.. This is no way to sell products or build a reputation.
I'd like to add my two cents to this. Here it is 2014 and I have been troubleshooting this issue on brand new Dell PC's we recently received. The new PC's all came with 82579LM adapters. I started getting most of the same issues reported in this thread and further more, on reboot or power on, if you logged in immediately after seeing the log in screen network connectivity would fail, with all sorts of errors in the event logs, mostly dealing with no DNS servers or Domain Controllers or Domains found, plus a slew of GPO and Profile errors because we use roaming profiles and folder redirection here. To be fair, I did have an older Dell PC here that displayed the same issues on boot up or reboot and it has a Broadcom adapter. There were basically 3 solutions that worked for me in resolving this issue.
1. For the intermittent drop from the network thru-out the day, I had to disable power management on both the Intel and the Broadcom, although the Broadcom never had issues of dropping the connection intermittent during the day it did suffer network issues coming out of sleep mode. Disabling power management fixed this issue.
2. For the Intel and Broadcom adapters, I had to configure spanning-tree portfast edge on each port for these PC's on my Cisco 6509 switch.
3. On the Intel adapters I downloaded and installed the most recent drivers, for me it is release 18.8, dated: 8/21/2013 and Version: 126.96.36.199. I had to turn on Wait for Link on the advanced tab of the NIC driver properties/configuration settings, Auto detect and Off did not work for me.
Once I did these things all seems well for about 2 weeks now. I'll update if in the near future this fails for me.