Have you set the DIR-655's WAN settings to PPPoE and entered the same username and password Verizon gave you for the DSL modem?
Connect to the DIR-655 at 192.168.0.1. Go to Setup, Internet, Manual Internet Connection Setup, set "My Internet Connection is:" to PPPoE, enter username, password, etc.
If you don't connect to Verizon via PPPoE, but use DHCP, then set "My Internet Connection is:" to "Dynamic IP (DHCP)" and press the "Clone Your PC's MAC Address" button at the bottom of the page (Verizon uses this to validate your connection for DHCP connections).
Press "Save Settings".
Make sure the DIR-655's WAN port is connected to the Verizon modem.
If the above doesn't work, get the MAC Address of your G90-6100 Modem (usually it's on a white sticker on the bottom of a modem, looks like 00:2B:34:43:A3:71, may or may not have ":"s in it) and enter it into "MAC Address:" (near the "Clone..." button), press "Save Settings".