If with two nics you have same problem, or you have no luck with these realtek nics
or this is a driver problem. Maybe something got corrupted when you did the upgrade,
or maybe some configuration was lost.
Is this the same driver (8139too) that you was using before the upgrade?
Realtek nics sometimes have clones that work with different drivers.
If you can, do a test with livecd (ubuntu, fedora, puppylinux) and see which driver
is loaded and if the problem remains.