Random Lag spikes/Disconnects

I am a real-time gamer. Usually there are seconds in the game that cant be missed, or your in bad shape. Well, I have a problem with a new modem that was installed Recently. I have a Linksys Router Wrt54gs ver.6, and a Modem given to me by comcast thats called Arris TM504G. Ever 10-25 minutes, it will send a lag spike, and mind you I have about 6 comps hooked up to this, and it happens to them all at the same time. It ranges from 3-15 seconds, then it sends all the packets at once. With my old modem, this didnt happen, and it was an actual Linksys modem, not arris. I would Appreciate if anyone could help me with this issue, or maybe guide me through some steps to solve it.

Things I've Tried-
-Connecting computer to the modem directly- I am not able to, because it shows a limited or no connection signal on the computer.

-Power Cycleing the router/modem- Doesnt help

Mod edit: Removed Profanity.