Just got a new PC with Asus Sabertooth Z77 mobo, having the same issue as many folks report here:
Asus Sabertooth Z77 motherboard, 16GB 1600 RAM, Intel i7-3770K CPU, Win 7 64bit Pro
EVGA GForce FTW GTX 670 w/2GB
Corsair Neutron GTX 240MB SATA III SSD + WD Caviar 2TB HDD
Connecting to a Time Warner provided UBEE DDW3612 cable modem and 4 port wireless router.
When I start the PC, I get an error ID: 27 in e1cexpress error that then fixes itself and everything connects at 1 gigabit, full duplex. However, during the day, I will get randomly disconnected from the internet. The network will disconnect, then anywhere from 10-20 seconds later reconnect again. No mention of anything in the event viewer which is unhelpful. Network speeds via multiple speed tests have been fine (20-30gb/s download, 3-4 upload). I have 3 other PC's connected via wire to the same router, 2 with ASUS Sabertooth X58 motherboards, none of them having this same issue. I have tried different cables, I have tried running the diagnostics for the Intel 82579V on-board adapter. I have also uninstalled all of the ASUS drivers, tried with the native Win 7 driver and also tried installing the ProWinX64 latest version (18.3). I have used the NVM tool (it tells me no update is needed). I have turned off all power savings options, added the BFlagToggle line to the registry, changed the side scaling and disabled Interrupt Moderation. I have also updated to the latest BIOS version from Asus. None of these changes have stopped the disconnects from happening. I'm considering purchasing a cheap PCI-e network adapter just so I can work without the disconnect issues.
Any ideas still unexplored?