wireless router drops connection speed from cable modem

So I'm using a Netgear CMD31T cable Modem into Netgear G54 Wireless Router WGR614v10. I had zero problems with this set up at my previous address, however at my new address I consistently get unusable connection speeds via the wifi (like 1 to 2Mbps).

I have had numerous calls back and forth with my service provider (Comcast), and they fiddle with things, have me connect directly to the cable modem, speedtest comes back higher than what I pay for, and they end the call. Problem is still not resolved, and this last attempt, I got a guy saying that the Netgear wireless modem is probably broken, and I shouldn't have more than 3 devices connected to the wireless router.

I seriously doubt the wifi should be trunkating the speed this much. I rarely have more than three devices connected and using the internet at the same time (typically the TV for netflix, a cell phone, and maybe a computer or second cell phone). I'm not looking for high speed either, just the speed of service that I pay for (about 12Mbps). And, I really don't think that the unit is broken.

So what could be causing the issue, and how to solve it? So what could be causing the issue, and how to solve it? Any ideas?