You can also try theTG852G. These gateways in my opinion are not the best. Like you said,"Poor wireless range".
If you want to keep the gateway you could call comcast Support for the gateways 1-800-363-2416 and ask for help in putting the gateway in bridge mode and then purchase yourself a wireless router and hook it up that would be the best.
What I mean by gateway is a router and modem. With a telephone line you are talking about a etma which is different. If you are looking to get a etma you can purchase one at Best Buy and then you will not be charged a monthly fee. If you want to buy the motorola sb6120 and a wireless router it will replace the rental from comcast.
I will include a link for you of the approved comcast modems.
Being that my only issue with this gateway is poor wifi signal range, whats your thoughts on a signal extender like the NETGEAR WN3000RP WiFi Range Extender that would just plug into an outlet on the opposite side of the wall that the gateway is in my office. I have tested the wireless signal there and it comes through the wall (i guess) real good and have nice strength. I would just like to boost it from that point to the room next to it. We are not talking a very long distance, just a couple rooms further from the office is fine and i like the idea that you just plug it into an outlet.