WNDR4500 keeps losing WAN connection with new RCA cable modem (Comcast)

[jwchatm]

I have been experiencing something odd. I have been using my WNDR4500 with the cable modem (Motorola) provided by Comcast for months without an issue. Recently I signed up for the Xfinity Triple Play package and had to switch to a new cable modem that had the built in phone router (RCA DoCSIS 3.0 modem). Every since then my speeds have been slower and my WNDR4500 keeps losing the WAN connection to the router. I am on the latest Netgear firmware (V1.0.1.6_1.0.24). Comcast has "reset" the modem several times and I have rebooted the router several times but get the same results. I am seeing some odd behavior. If I plug my PC directly into the cable modem I get an address in the 67.x.x.x subnet and have no disconnect problems. (BTW...this IP is in the same subnet I was getting on the router when on the old cable modem.) The odd thing is that when I plug the router into the new RCA cable modem, it gets an IP in the 77.x.x.x subnet. Why would the subnet be different on the router than on the PC? At first I thought Comcast was determining which DHCP scope to lease out of based on device type (ie: routers get 77.x.x.x and NICs get 67.x.x.x) but if I clone my PC MAC address on the router it still gets the 77.x.x.x address. It seems as though the WAN DHCP client in the router is behaving incorrectly. I may be over-analyzing this but I cannot account for the WAN disconnects or the strange DHCP behavior. Has anyone else seen this? Is there a know issue between the WNDR4500 and the new RCA cable modems with phone service that Comcast is issuing? I could use some experienced insight here. I am using the ready print feature to share my laser printer and UPNP is enabled because I am running a media server from a hard drive plugged into the router. I have no issues with these services and the streaming is awesome.