I have an almost identical setup as the OP. I have FIOS 15/5 and a PAP2. When I first started with VOIPo I had all kinds of problems. Late in December I removed and replaced my FIOS ACTIONTEC Router with my old Buffalo WHR-HP-G54 router loaded with DD-WRT. 95% of my problems went away.

I Still have an occasional problem, but they are much less then before. The occasional ECHO issue will never go away. As our fearless leader, Tim, would say, "That's the nature of voip."

If you're using the Actiontec router I would strongly suggest swapping it out for a "normal" router. You will have to contact Verizon and have them switch you over to ethernet at your ONT)on the side of, or inside your house and get rid of MOCA. If you also have FIOS TV (I do not) it is a little more involved but can still be done. Check out the Verizon Fiber Forum over on DSLreports.COM.

For those not familiar with FIOS they use no "cable modem."