If your signal is dropping, you will need to see if the problem is with the router in general or just the wireless portion of your network. The Rev. D has been around for a while, so you could call Verizon and request a new router. Chances are good that you will receive a Rev. F or a Rev. I router without charge after reporting issues with the router.
If the Rev. D has been suiting your needs otherwise, I would start off by checking your connection through the wired network first. If everything is stable we can try changing some wireless settings around to improve connection reliability