Heya ;>

I had the exact same problem as you, when the net upgrade came out, i checked my speed and it was still stuck on 512. I tried over and over, but it didn't budge ;/

However, I finally got it fixed. Please note I dunno if this procedure will work for you, but I'm here to help

I have the exact same router as you do.

Go to your linksys homepage (192.168.1.1) then click on administration, then "Restore to factory settings"

Once this is done, make sure you have your CD that came with the router, otherwise download the software

Load the CD and do the steps from there

What I saw was my connection went from PPPoE to PPPoA, I'm not really familiar with those settings but it did all automatically, I checked, and my net speed doubled ;D

Hope this helps =]