How long has that Netgear FVS318 been around? I have a "pull" from a
client's office that flaked out similarly to what you described after 3 or 4
years. I did update the firmware and continue to use it on a non-essential
network segment (my bench, easily swapped out), but I can't say I trust
it.
You might try a different gateway...
p.s. -- the standard 4 pings isn't going to tell you much. Ping is your friend. :)