New Router not getting IP address from Modem

I am replacing an TP Link 450M with a AC1750. The new router is not getting an IP address from the modem; Zoom 5370. I first thought that the "internet" port was bad on the 1750. This is not the case. I "hard reset" the modem. I tried MAC Clone; "Use the current computer's MAC Address"  I also can not communicate with the modem directly connected with a laptop for more then a minute before dropping the IP. Only with the "old" router am I getting and keeping an IP. Does Comcast require the router's MAC address? I can't think of anything else that would cause this. Comcast was less then helpful last night. Thanks for any help or insight that may be offered.