Hey,
I'm having almost the same exact problem your having.
And with an SMC Barricade Router as well.
SMC7004BR
But the funny thing is,everything was running smooth for months and months with no problems.but then it seems after the RR connection came back up after it was down for a few hours,i noticed my Pings jumping over 100.when it stayed around 40 for months and months.
Then i decided to check my speeds at Speakeasy and noticed another problem.
I was getting 3m/500 (Down/Up) before,but now it was only showing around 1M/120.
Just seems odd everything was working fine for a long time.
then out of the blue this happens.
I believe its either the Cable Modem went bad somehow and is not able to support 2 PC's,or perhaps the Router went bad.
Heres a link on my Post:
Right here
If you manage to figure the problem out,let me know.
Shawn.