Frequent Disconnects On Cable / Router

The internet connects fine, but every couple of minutes it will disconnect for a couple of seconds. It's not a big deal when browsing, but it's disastrous when downloading big files or playing online games.What I've tried so far:

-Resetting the modem. No change.
-Reconnecting the modem/router completely. No change.
-Replacing the main splitter. Slight change, but problem came back eventually.
--Original problem came with the tech's 2 way 5-1002 mhz spliiter.
--I tried replacing it with a 3 way 5-1000 one. The modem on 7db and cable on 7db. It worked fine for a couple of days.
--Problem comes back today. Moving the modem to any of the 3 outputs doesn't fix anything. Moving it to 3.5db actually causes a short timeout every minute when I try to ping yahoo (as a test).
--I've also tried a 2 way 5-900 mhz splitter. It was the worse one of all.

Other info:The internet went down to the entire block at the start of the year. No one knew this of back then so we made a call to comcast, and they scheduled for a tech. A couple days later, we decide to get a new modem from the comcast center just to make sure it wasn't our modem. Some problems with activation prevents us from knowing if it was. We get back online somehow the next day, which is also the same time the tech came. He decides our numbers are weird and adds in a splitter for the internet and tv (which leads into another splitter for each room), and an amplifier for the tv. In the middle of this, another tech stops by and tells us the entire block was down and he said he fixed it now, he doesn't stay long. The first tech finishes installing everything and leaves. All is fine for a couple of days, until a week later and we start experiencing frequent disconnects. We've tried calling comcast again, but they say the connection is fine on their end and the problem is with our router. When I ping the router and the modem directly, there are no dropped connections. It's only when I try to ping anything on the internet when the problem pops up.