If you are using a shub in modem mode, your pc is directly connect to the shub on port 1 as the sole device and you are still experiencing lag then getting a new router won't fix it for you; there are other issues afoot.
Although a modem is a modem, you can't buy your own (like you can a router) and use it on VM's network. There is some nitty gritty security stuff going on in the background and all modems (even when they supplied standalone ones) have to be VM supplied. These days everything is a shub in one form or another.
I think you should set up a
TBB ping monitor because I am interested to see how pretty your graph is going to be. Once it is setup post it in here and we can look at it in real time.