The wireless on the CGN3, while OK (better than their other ones).. it still leaves some to be desired.
Getting a better router, and putting in bridged mode, would likely improve it greatly.
But even to begin with, there might be a few things to tweek on the built in, to get better speeds. There can be things that are limiting it.
A) what device are you connecting to the CGN3? (this will make a diff on what type of card it has, etc)
B) How is the signal strength?
We can go from there, and change a few of the wireless settings, which can slow things down (but make it more legacy compatable)