Motorola Surfboard Sb5101 Modem / Random Connection Drops?

I have a Motorola surfboard sb5101. Provider is comcast.I have never had any problem with my equipment until now. Here is whats going on. I bought a used sb5101 a week ago so that I would not have to pay the rental fee anymore. Comcast activated it, and it worked fine for a week or two. The other night I got disconnected from XBOX live randomly in the middle of a game. Thought maybe just a hickup, no biggie. Well it happened 3 more times in a few hours, then again the next day.So thinking maybe this used modem is bad, I plugged back in the rental from comcast which I still had. Worked fine for a while, then the same thing, random dissconnects after 10 min, 30 min, 2 hrs into a game...etcOn both modems, the 1st and 4th green light are solid, the 2nd and 3rd green light are flashing when the connection from LIVE drops.So I'm starting to think know that neither of the modems are bad. I then try going directly to the modem instead of the router, never had any problems with the router but figured I try.I even went into the attic and got rid of the 4 way splitter that feeds cable into all the bedrooms and put in a 2 way instead hooking up only the cable line im using for xbox. Thought maybe the signal is getting degraded to bad, eventhough never had a problem before.So now I'm practically hooked up right to the line coming off the street, ethernet cord plugged directly into the modem, no router. Still dropping connections randomly with same 2nd and 3rd light flashing.The connection needs to be completely stable for multiple hours.Also, I called comcast when I had to reactivate the rental modem, so they did refreshed that modem and reactivate it, but still had the disconnects the next day.