Can't get SB6121 to work well with Mediacom

I've had the SB6121 for a few months now. At first it seemed great, then I started getting random disconnects. Signal levels all look good. I've since upgraded my Mediacom account to 50/5 and the modem will not bond to more than one channel. I get more like 30/5 and still random disconnects. They tried pushing through firmware, but it won't accept it. Anyone have these type of problems??