Modem Restarts Constantly

I have a Motorola SB5120 modem and it has been turning off and on constantly for past few months. Multiple techs have come to look at my connection and each one said the problem was fixed, but my modem still restarts all the time. Downloading large files almost always makes it restart, but other times it seems to restart at random, regardless of what I'm doing.

My upstream power level is also very high and sits at about 54 all day, but can also fluctuate rapidly. A tech came and installed some kind of attenuator, but it didn't fix the problem. Phone support, without even going over my modem logs or stats, just immediately told me my modem was bad, but I'm not ready to spend money on a docsis 3.0 modem without being absolutely sure it will fix the problem.